I have complied a list of rules
here.
This will be a good opportunity to play with friends in a fun game mode without some of the many broken things in this game.
This will be a good opportunity to improve at the game and learn how to play skirmish.
Here are a few tips for skirmish:
Angles and positioning are everything ...
Holding good map position (you have to learn these spots for every map) is a key to winning when its 3v3 in skirmish. You don't have to go and chase the enemy unless you have an advantage (2v3 or 1v3). If your opponents spawn on opposite sides of the map it may be a good idea to push your advantage before someone flanks you.
Try not to be in the same lanes (lines of sight) as your teammates when possible, opens you up to both getting grenade-d and may allow you to get flanked. If you can't get another good lane stand behind your opponent and tell him to back up if he needs and you can get his support if he gets rushed (make sure you stay out of the range that you both could be grenade-d (think just outside of arc bolt range).
If you are in a bad situation, it is OK to run and hide. You want to always have your gunfights near cover so if you start to lose you can back out before you let your opponent get the kill. If it is 1v3, you can run to the back of the map and hope your teammates spawn near you. Just try to play smart.
Think about team positioning. It is ok to be far apart from each other and have different lanes, but you don't want an opponent in between you and your teammates because it pretty much guarantees you are going to get shot in the back by someone, try to prevent this.
If you split spawn (opposite side of the map from your teammates), try to stay alive and communicate with your team to try to get closer to each other.
A lot of these things also apply to trials, but you want to be even more cautious because one death can really screw over your team.