There's no question that you have to take your lumps early on. The weapon upgrades make a big difference, but at least 50% of it is learning the maps and learning how to play (beyond your class specifics.)

Lots of beginning players pay no attention to spotting (either doing it, or responding to spotted players.) They run around like deathmatchers, right down the middle of streets. They sit in stationary gun positions way too long. They fail to repair vehicles. They shoot tanks from the front. They fire from a window, back away, and then go right back to the same window to shoot from again. They fail to take into account bullet drop. They forget the grenade, the knife, the pistol.

There's little tricks that you pick up on that only come through playing. When to stop and look, when to move. Just keep after it.