This is just based on observations in the campaign servers over the past week or so, so take it for what it is.
1: Control your team spread.
2: Watch your fires.
3: Watch your team movement.
4: watch your team positions.
5: Time your gunfights.
6: Use the terrain to your advantage
7: consider alternatives
8: know your weapons
on 1: 1-0 players should keep an eye on the position of their respective teams. It's better to arrive at an objective or an LZ with an entire team at once instead of the entire group strung out. This is also important for the demolition guys as they are the ones trying to slow down pursuit with mines. It doesn't help if the team medic needs to revive a team member that has been taken out by a mine from his own team.
on 2: Not only do you need to watch where you're shooting, it doesn't hurt if you watch were your team is shooting and try and help out. But beware, other enemies may try and sneak up on you, requiring you to shift your focus elsewhere.
on 3: Don't always run. It doesn't hurt to walk for a bit. it might also help with your and your team's stamina. Also, be aware that you make a lot of noise when you run. Noise travels...
on 4: Just like at point 1. Keep an eye out where everybody's at. This is esspecially important when boarding the single entrance door Kingbee chopper!
on 5: you don't always need to engage the enemy. Sometimes it's better to just fade away without having fired a shot. This also helps you conserve ammo which you might need later.
on 6: Make use of the terrain features. Putting some jungle and rocks and trees between yourself and flying bullets helps in case of pursuit, but it can also conceal your approach. Also, the terrain
can be used to hide bodies. It can be fun to try and leave a toe popper nearby incase anyone comes looking for missing people..
on 7: Now I know it's nice to rejoin your team by way of the Kingbee if you end up respawning at base, and I also it's kind of nice to fly a Kingbee back to an LZ incase you need to make an escape
but, it attracts attention when you do not want to attract attention. Same thing with run and gun battles, they sound exciting from time to time but, it could be interesting for an entire team to have supressed weapons and try and ambush trackers for example.
on 8: Know your weapons. This isn't really about marksmanship, but it is about knowing what else to do with the gear you've got with you. For example, it's fairly obvious that you can stop a truck and an APC/IFV with a LAW, but it should also be obvious that you could try and lob a grenade from that xm148 you're carrying through the slit of a machine gun bunker. In this manner I could also adress people that like to play the demolition class. It doesn't hurt to use a couple of claymores to create a 'killbox' on your backtrail to 'discourage' pursuit.