Partially tactics, partially guidelines.1. Do not get out of your vehicle unless you are safe and near your guard tower.
2. Rushes (APC): organize ahead of time, not while in route. Pick a target (or targets if a bunch of APCs are going, for instance) and go there. Try not to be noticed. Don't shoot at enemies, rocks, trees, the sky, etc. unless overcome by enemies in which case you're not going to make it to your target anyway. Head straight for the target building and don't stop. Someone with bad lag shouldn't drive the APC. Go in one by one.. less chance of mines killing everyone. Then straight to the MCT to place timed C4. Stay and defend it for a while.
3. Do not get out of your vehicle unless you are safe and near your guard tower.
4. Offensive rushes (tanks): Again, plan before everyone heads on. Then when the signal is given, don't hesitate. Just go towards the target and shoot. Don't stop, don't back up, don't shoot anything else.
5. Do not get out of your vehicle unless you are safe and near your guard tower.
6. Once 350 credits are available, make sure that someone's placing mines (in proper places). I often do it myself if no one else appears to be. On some maps, it's critical that this is done as soon as possible. It's scary how many maps I join in on and no one has put any mines down 5 minutes into the game.
7. Do not get out of your vehicle unless you are safe and near your guard tower.
8. Never leave your base completely undefended, regardless of any situation. Sounds stupid, but I've seen it done faaaaar two often.
9. Don't shoot large vehicles with your pistol. Find something.. anything.. more useful to do. If close enough, the pistol will do noticeable damage to a heli, though.
10. Do not get out of your vehicle unless you are safe and near your guard tower.
11. If you're an engineer/tech/hotwire, don't use the repair gun to "attack" the enemy. All it does is repair them and really annoys your teammates.
12. When placing C4 on the MCT of an enemy building, try not to attract attention until after the timed c4 goes off. Then detonate your remote c4 (if you have it) and whatever else. It gives the enemy team very little time to protect the building.
13. Aim for the head. This includes vehicles where applicable. If you're in a tank and see a sniper or raveshaw in a corner, try aiming for their head and you can kill them in one hit. On the counter side of this, don't stand still if you can help it. Jump and move around while repairing vehicles on the battlefield.. you'll live longer (although you might look weird to other people).
And finally..
14. Do not get out of your vehicle unless you are safe and near your guard tower.
There are obviously a ton more tips/guidelines that could be posted, but these are some problems that I am encountering in at least every other game. It's clear that a lot of people don't know. Unfortunately, I bet that most of them don't read these forums.