So coming to the end of my first two sets of multiplayer games, and some things I have learned about specific strategy that I have seen scattered around the forums or learned myself, but havent seen summarized anywhere. If any of you players have anything to add or discuss, please feel free.
1. Research. Infantry weapons are king, as is doctrine. Everyone should research infantry weapons (and tanks and aircraft if used by that major) as the very first priority, and then its accompanying doctrine as the second. Didnt really realize how powerful armored doctrine is, but if you are using tanks and mechanized units, that second attack is very strong. Long range aircraft and ground attack exponentially increase the power of airpower both against air and ground targets as well by the late game, therefore that should also be a priority for any nation relying on airpower (Germany, Japan, US and UK). Also, command and control is very potent as it increases the command rating of all of your headquarters in addition to the number of units they can command.
2. Air power is quite a force multiplier early war, and a war winner by 1943. Tactical and medium bombers upgraded are good in a counter air and ground interdiction role, while Strategic bombers are exceptionally good at supply disruption... they also are fairly effective against ground units in a pinch as well.
3. Naval warfare. Combined arms teams is usually the best way to go, with a combination of ground based air, surface naval units and submarines. The submarines serve a scouting and ambushing role, air power (ground and naval based) inflicting most of the damage and the surface fleet attacking carriers or finishing off crippled naval units. Naval units should usually be committed with supporting air power, and an land/naval based airpower combo will generally be stronger then a solely naval based equivalent.
4. Country strategies
Russia. The only way to play is to rush infantry, tanks and the accompanying doctrines (infantry and armor as well). After that I now develop mobility, then industry, production, anti-air (2 levels) and command and control. The only units purchased before Barbarossa are headquarters (the bonuses are key to letting your units hold the line and counterattack deep inside of Russia) and maybe a 2nd engineer. When barbarossa is launched, the idea is to withdraw, only delaying the Germans, but not standing and fighting until the Germans are low on supply in the mud or snow. Preserving your forces and increasing the unit density is the most important thing you can do until your counterattack. The turn the Germans invade the allies should maximize their convoy aid to the Soviets to assist in building their units, and force marching the starting units from Siberia from the start of the game can also help (they arent enough to defend Siberia anyways, and can help a lot in europe). I've seen varying uses for fortifications, helping to defend in front of leningrad, moscow, or the Caucasus mountains... basically wherever you need a shield. If you build in the center or south you can use it for a counterattack... in the north it seems mostly defensive in nature. Finally, a note on reconstruction... I normally dont build any new units as Russia with the mobility upgrade, but any unit I reconstruct I produce with it, leading to dramatically increased mobility later in the war.
First, infantry weapons and infantry doctrine are the two most important techs here. Thinking on it, I think production, command and control and anti-air (up to level 2) are also good to dump any spare points into. China can go either offensive or defensive... against an experienced player I would argue playing mostly defensive is a better option. Build a series of fortified lines with your engineer and make the Japanese player come to attack you in the mountains and pay for every hex he takes and hang on. Artillery can also be useful if the MPP can be spared. If you can hold Nanning until France falls you can just march into French indochina, although this is situational as it will flip thailand to the Japanese. If you choose to go offensive, find a place where the Japanese player cant form a continuous front and throw your units into the attack to isolate units, attack aircraft and headquarters. If you restrict the amount of space the Japanese player has to manuever (easiest in the south) then they will find it difficult to make attacks. This is a high risk-high reward strategy though. If you choose an offensive strategy and things go badly, you will end up losing china.
For the US I research everything, starting with the 1 chit techs (infantry weapons, tanks, fighters and ground attack) followed by naval weapons, industry and production (arsenal of democracy after all) ASW, anti-aircraft to level 2 for units and ships, amphibious assault and long range aircraft. The united states is all about keeping the allies in the game with Lend Lease and limited attacks around the periphery (north africa, Japanese island chains, etc) until it can build up a large enough army and air force to go up against the Germans in Europe. Navally the United States probably needs a few more fleet carriers, all of its 6 escort carriers, and destroyers, as well as all 4 naval bombers. An American player should be very wary of an invasion of hawaii at the start, and should counter by staging its 2 upgraded starting armies there, with upgraded fighters and naval bombers ready to operationally move in on the first turn after a Japanese attack. If this doesnt happen you can go right over to the offensive with your existing forces. If it does happen, then you are in a good position to hold hawai and give the Japanese fleet a good bloody nose while you are at it (while limiting their attacks elsewhere because they have to put a lot into this attack). After that just make sure that you build up enough combat power to enter Europe in force... dont launch a premature invasion that is crushed (time is often a factor here as the Soviet Union will be under extreme pressure... resist that urge to act until you have sufficient ground and air power) because it will take too long to rebuild all of those low supply invasion forces for a second try.
Britain. Britain is in it from the beginning, and has to prioritize. For research, infantry weapons first of course. I would then argue fighters, ground attack, tanks, doctrines, ASW, Long Range Aircraft, anti-air to level 2, and command and control are all important. Once you have some breathing space, investing in invasion techs will let you launch invasions of your own, although it is possible to only use US units for that. Unlike the United States, industrial strength only increases resource gain by 10% (instead of 20, or 15 for Germany and Russia) so I usually do this last. As for builds, have the BEF in a place where you can extract it easily before the fall of France. Keep at least some regular units in England, otherwise you are vulnerable to a 1940 Sealion (especially if your carriers are in the mediterranian). Up to you, but I think a decent strategy is to commit reinforcements to north Africa, and build an engineer first thing and have it build fortifications.... will make an axis push to the Suez much harder. Typically I've seen the english put the bulk of their carriers into the mediterrian to try and destroy the italian fleet in their ports while they still have the French fleet as cannon fodder. A decision also needs to be made in 1941 about whether the british will try to contest the Indian Ocean against the Japanese... generally the japanese fleet is superior, so if you do this, do it right and commit enough to be effective. Other then that, navally you should probably have two sub hunter groups by mid-41, one to protect the convoys to Russia, and the other in the Atlantic or the med wherever the Germans have committed their subs. The most important thing to do as the British is to remember all of your assets and using them. You have a lot of units sitting around the world (some fleet units in australia/new Zealand, free french Corp in africa, south African army etc) but unless you can reinforce, upgrade, and bring them together in support of your overall objectives they will be useless.
France. This nation has a shelf life, and all the players know it... so use it! Inflicting as much damage as possible in MPPs and time is what the French have to contribute, so you can play around with them a bit. Build cavalry or anti-air, or another Corp or 2. Whatever you want really that you think will buy a few more turns. Just a couple of things to remember. 1st, when Belgium falls, Italy will enter the war, so you need to guard the south with at least 2 Corp. 2nd, France gets some nasty morale penalties when the Maginot line gets penetrated or flanked, so choosing when, or if, to abandon maginot is an important choice. Finally, france starts with 2 armies in Maginot... not really necessary. You have corps that can hold the fortified line just as well. If Germany is not trying to break through Strasbourg, it is possible to replace both those armies with corps to help strengthen the fight in the low countries.
India. The last and weakest of the allied majors, India supplements Britain's strategy. Research should be focused around infantry, maybe with armor and aircraft included. After that, where you focus your energy depends on Britains overall strategy. East Africa, Middle East, Burma, Dutch East indies are all places the indian army can make a difference.
Germany. What germany does will largely decide the game. Research should prioritize infantry weapons, fighters, tanks, long range aircraft... after that, it depends on where you are going. Germany takes Poland, and can choose to attack France anytime before June of 1940 (flexibility here, although I usually prefer earlier to later). After that, Germany needs to choose North Africa, Soviet Union, or a 1940 Sealion. Keep in mind if Germany does Sealion, then Russia is entering the war in mid-41, so plan accordingly. Going to North Africa and making it to the Suez also speeds up this timeline, as does bringing spain or turkey into the war. Dont forget to focus on diplomacy as Germany... Yugoslavia is possible if you invest early enough, as is Turkey or Spain, but you need to prioritize one of them at a time. Continously expand and improve your airpower and build out your armor to remain relevant, and whichever strategic direction you go, go all in to achieve a decisive result.
Italy. Italy is an adjunct to Germany's strategy. Research infantry weapons, doctrine and whatever else interests you. Remember, when the allies enter italy there are some sever national morale penalties, so after a point if the med isnt secure you will need to garrison that soft underbelly.
And finally Japan. Research infantry weapons, doctrine, aircraft and long range aircraft. ASW and anti aircraft is also important (although allied subs usually wont be as upgraded as German ones, so you dont need to go crazy with the ASW. You have until 1941 to focus on China, and should use everything you have to get them on the ropes by the time you go to war with the west. You really have a lot of different strategies, but a few effective ones are as follows. First, Hawaii first. This requires a fairly strong attack with marines in case the island I'd garrisoned, along with the bulk of your fleet. It means your co-prosperity sphere will take a bit more time to carve out, but you should be able to snap up the rest at your own pace. At a minimum you need to take the philippines and dutch Indonesia as well in these first attacks, because if the Allies can fortify these areas they can be hard to dig out. Second is an india strategy. Usually employed after attacking pearl harbor, this requires the bulk of your fleet and marines, and should usually only be pursued if you see the indian army all over the place (as it is probably not in India). Third is an Australia strategy. This will require a fair amount of marines and most of your fleet, because australia is a very big land to take, and massing local supermajorities can be hard even with overall superiority. Finally is the decision to go to war with the Soviet Union. Probably only a good idea to do this if things are going well in China and you can divert the necessary units to attack through Mongolia as well. Otherwise it wont tie down that many Russians and will hamper your ability to do other things.
Anyways, I hope this is a decent rollup... most of this is from my lessons learned from my first set of multiplayer games, played through to their almost conclusions against a pair of players far more skilled then I was when I started. If anyone disagrees with me or has things to add, I would encourage that, because good discussion is a good thing.