One of the easiest and quickest ways to improve your bbq is to begin documenting your cooking sessions in a bbq journal. A spiral notebook or three ring binder will work well. Some also use a computer document instead of pen and paper, but it's not quite as portable unless you have a laptop.
At contests, I keep a journal for each meat. I keep track of everything following the arrival at the contest. I pay attention to the time we prepare each meat for marinating. I carefully document the cooking start times for each meat, the weather conditions, the outside temperature, and the cooker temperatures.
I also document the critical times for the various meats. For example, I start my briskets fat side up and document the time I flip them to fat side down. (This particular tip has paid big dividends for me in contest winnings.) I document the times I spray the various cuts with apple juice. I pay particular attention to when I wrap the briskets and pork butts with aluminum foil.
After a few cooking sessions, you'll be able to improve your results dramatically by tweaking your start times, temperatures, and methods based on your historic results. Barbecue is more art than science, but anytime you can add a little science to the art, it will reap dividends in the long run.