There is not much that France or England can do to help Lux, Belgium, or Holland whenever the axis attack. Here are the few things that could be done though.
1. Position the RAF and French fighters so that they may fly defensive air support for Belgium or Holland. It is not certain that they will intercept though. Make sure the fighters are attached to an HQ.
2. Evacuate the Netherlands Navy to British ports if Holland doesn’t fall the first turn or use them against KM if ship is able to be attacked. There is a chance that the Dutch navy will join the allies even if Holland falls.
3. If for some reason the axis fail to take Belgium on the first turn. Reinforce the Army in Brussels to 10.
4. Use an allied corps to take back the factory in western Brussels and withdraw corps. This takes away MPPs from Germany.
5. Sending Allied forces into Belgium or Holland is not a good idea, as forces will not be entrenched and will get wiped out by Luftwaffe and German ground forces.
6. Use any allied ships to do shore bombardment of any German forces that are along the coast, hit and run with the ships though, as need to avoid losing Royal Navy to German bombers or subs.
For Strasbourg defense? Are we talking Strasbourg or hex south of it? Or Metz forts? Taking Strasbourg doesn’t generally allow for fast axis advance. Taking Metz along with Luxembourg is generally the more dangerous thing for France to worry about.
1. Strasbourg is defended by a full strength French Army. There is not much you can do better than that. Make sure that it is attached to the French HQ.
2. On turn one for the allies, attach HQ above and do spoiling attack on one of the German Corps if odds show defender loses 1. Bring British AA gun at Malta to France, but make sure you garrison Malta.
3. Put the AA gun up by Metz or Strasbourg depending on where Germans are massed. This will dissuade Luftwaffe attacks.
4. Make sure that you put French Corps all along the Belgium/ French border up to Lille. Make sure Lille is defendied.
5. Try to position French Army units behind Corps defenses for counterattacking any overextended axis forces. If possibly get British and French tac air reinforced and use them for counterattack too.
6. Make sure that the French Air Force and RAF are based around Paris with HQ attached. The supply around Paris is like 11 or 10. This combined with HQ leads to better morale and combat effectiveness. This goes for the Tac Air too. But you have to make sure that reposition and defend Paris as Germans approach.
7. Depending on what your allied strategy is going to be, you could use one or two of the British Carriers to help defend and with counterattack in France. Again, be careful about subs and Luftwaffe.
8. Because France no longer surrenders automatically upon the fall of Paris, make sure that you garrison Marseilles, Lyon, and put a garrison unit in Bordeaux.
9. Do not let the French units in the Maginot line get surrounded. SR them out before that happens.
10. France will eventually fall, but you want to make it a long battle with cost to the axis. Do a fighting withdrawal at times to slow down the destruction of the French Army.
11. Have the British forces defend the Amiens area and North of Paris. Try to not let the entire BEF get destroyed in France, as it nice to have them for defending England.
12. I have seen some folks put the British Corps up forward early on in the defense of France though, as they can be quickly rebuilt to defend England.
I hope this helps.