My first marathon was just under 2:40, at the age of 22. I didn't break 2:30 until my fourth marathon, at the age of 24. After some years of very sporadic training and racing during my mid- to late-20s, I ran 2:20, then 2:19, then 2:18, all on record-quality courses, and all after turning 30.
People will give you all kinds of advice about interval workouts and such, but you'll almost certainly get your biggest bang for the buck by focusing on increasing training mileage. My biggest improvement came during a period of absolutely no racing, interval training, or speedwork -- just putting in as much mileage as I could handle. The only really high-intensity training I did during that time was "cross-training," primarily pool-running, along with some stationary cycling. The focus was on increasing and maintaining metabolic stress while minimizing the kinds of musculosketetal stresses that lead to injury or, at the least, require periods of reduced training volume.
If you are serious about qualifying for the trials for the 2012 team, you will -- in my opinion -- maximize your chances by avoiding the distractions of various intermediate racing goals along the way, focusing entirely on that single goal. Most people don't do that. They want to run lots of races along the way, sometimes just because they want to check out their progress. Although it is certainly possible to improve tremendously in a program that includes regular racing -- indeed, that's a very typical approach -- I don't believe that it is the optimal use of your time and energy in your particular circumstances and for your particular goal of qualifying for the upcoming Olympic trials. You need a sustained period of the kind of metabolic stress and gradual adaptation to musculoskeletal stress that comes from high-volume training without the loading forces and training interruptions or volume fluctuations that characterize most programs that include regular racing. Also, if you have a very busy schedule outside of running, you will find that regular racing is an extremely inefficient use of your time if you're trying to maintain high training volume.
I would suggest that your first training goal should be to increase training volume to 100 mpw or more. Don't worry about pace; just worry about volume and injury-avoidance. After you adapt to the increased volume, you can increase training pace, but continue to stay away from higher-intensity interval training and racing. You can add in long-interval sessions (like mile repeats) later, but you're nowhere near the point where that would be optimal right now for the rather ambitious goal that you've set for yourself. Even then, I would probably choose to introduce "tempo" or "threshold" training (at an intensity that may approach half-marathon pace) before interval training.