Once the game gets going, I tend to switch to defensive mode. At the beginning, though, I'll usually join in on the initial tank rushes and offensive combat.I prefer GDI and usually use medium tanks. Typically, my self-assigned role is to hold back and protect the base from any incoming attacks. Favorite activities.. ramming APVs and beating the snot out of them before they can get near the base and running over all the passsengers.. Too bad ramming doesn't do damage. Anyway, by sticking around the base in my medium tank I am usually able to stop engineer/nuke rushes on most levels (some are nearly impossible to defend against).
My absolute favorite activity is to walk up behind snipers and attach C4 to the back of their head.. or their face if they turn around. Preferrably timed C4 so I can watch them run around with it stuck to their head. It's tough to do though and usually their are more important things to do, but sometimes the opportunity presents itself.
My ping time is usually to high to allow me to do much with a sniper, but I don't really like sniping in this game anyway. I find tanks and infantry battles much more fun. I turn to Unreal for all of my sniping needs. The one exception is that I do use a sniper at times to take out artillery or missle launching units. It's very effective and they usually can never locate you before it's too late. This obviously works best with the lesser of the two sniper units.
My most successful tactic is to take an APV into the enemy base and place a beacon, then park the vehicle on it and shoot/smoosh anyone that comes near. Only works if no one sees exactly where you went, so sometimes I have to hide until their base is mostly empty of units.
My most preferred infantry unit is the black hand rapid laser guy.. good against everything. For GDI, I'm usually an engineer or hotwire.
Anyway.. that's how I often play. It might chance once I get a faster connection (should be next week).