As a player who also sucks, I can tell you that you probably don't really need any of the things listed in the thread. They'll help, but they're more for competitive players working on their aim. What you need is to play.
Seriously, just playing the game is the biggest factor in how well you do. You'll develop gamesense and aim in a setting that fits your skill level by just putting in time on a pub. Once you've got the basics down, you'll be able to move up to more focused training in MGE or a Newbie Mix.
You should remember to play smart when you pub. Keep track of your kill/death, and if you die a lot, brainstorm what would be causing it. One tip which I suspect might be the issue: when you go into a fight, count the players involved from each team. You're probably dying to pairs or groups of players while the rest of your team backs off.