I've been lifting weights for about three years. I didn't gain as much mass as I could have at first because I didn't use the best form or technique. I've grown much wiser as to the best way to lift, and how to increase muscle mass.
The most effective way to gain mass quick is to shock the living day lights out of your muscles. What I mean by that is combining endurance training with power training. One day, use a ton of weight with only a few reps. The next day, use a light weight, and a bunch of reps. The key is not to let your muscles get adjusted to any set routine. By variating your workouts, you'll experience extensive growth. I gained an inch on my biceps in about three months using this system.
Muscle & Fitness has a bunch of helpful tips on the best way to train. This is where I found the awesome strategy I mentioned above. I'll try to find links to more bodybuilding pages. If you have any weightlifting strategies that work for you, let me know . I'm game for any new way to lift.