Skirmish isn't hard. I went in solo and did perfectly fine. (Especially considering that 3s aren't my strong suit) Don't play only 6s if possible. You won't improve that way. Skirmish and Rumble work on your skills a lot more. Clash and other related 6s modes can be mastered pretty easily because it's so easy to catch someone off guard in the chaos of having 12 people all fighting each other. This isn't really gun skill, and I've had games where I go positive just because I'm catching multiple people off guard, not because I'm actually winning any 1v1s. In Skirmish (and to a lesser extent - Rumble), you're forced to fight a lot more 1v1s -- you don't get nearly as much of a benefit when it comes to teamshots or off-guard opponents. It forces you to fight someone who's looking at you rather than getting the first shot off on someone who isn't paying attention. Keep giving it a try, and with a fireteam if you have to. But if you want to improve your skill, Skirmish is a great place to start.