How to get better at MW2 online?

A couple of days ago, I was PWNING online, almost every game, I'd be getting at least 2 Harriers, having more than ten more kills than deaths and just controlling the match. But today, I was sucking, I'd always die before even getting a UAV and I'd be lucky to end a game with 8 kills 8 deaths. Any advice? It's pissing me off!!!