Definitely play MA live. It will blow you away. The competition is tough and I do recommend creating your own games that you can control with your friends. That way you can all improve together and then venture out occaisionally to the harsh reality of MA Live...
From what I have seen, there is a learning curve to these games. Kids with lots of time have really progressed along the curve...Besides the tough competition, there is "cheating" that goes on. What I mean is, kids will form secret teams in non-team games and just wait for you to reespawn, then blast you - ten times in a row. All to improve their stats. You can set up games to give yourself the advantage, or to make things fair. The "cheating" can get annoying and discouraging pretty fast!
I am learning that it may be best to observe when you can at times. Some games allow you to host a game and be observer. You can cycle through and see what tohers are doing, what their strategy is. On Ghost recon, a guy waited in a room all game to be the "last man standing". Then he got killed!
Also strategy changes of course from single player to multiplayer. The desire to run in and shoot someone usually should be overcome! Reading the forums and websites helps too. The problem for adults is not enough time.
We should get a group or groups together for several of the games, and maybe have a little schedule. We can bring in some of our friends who are not on the forum as well. Its also cool to chat with people in Live, which you can do without even playing!