Quite new to the whole PBEM thing myself! I don't know that there are preferred house rules, one that is coomonly established is to restrict the use of artillery on the first turn and on the deployment zones.
Then, it's on a per-game basis, you could restrict the use of TRPs in Meeting engagements, limit the armor ratio in a given force, limit the use of APS equipped vehicles, and so on.
In any case, I'm also here for the fun first!