well.. with any side you need assualt troops imo. upgrade them and they are good at fighting troops, tanks and trenches, dont bother with snipers or generals either.
I just keep machine gunners in my trench until the later battles with no trenches where I pretty much keep sending tanks or on the last where enemy has trench assault ftw.
Assault troops are argueably the most valuable infantry units on the battlefiled. Deploy as many as you can. Keep machine gunners in trenches as much as possible. If there aren't many trenches, hold your ground and bring their moral down. If there are many trenches, when the area is clear break for the next one. Leave your trench immediately if the enemies call an artillery strike. This all applies for the German and British campaign.