The world of pro gaming is incredibly competitive. If you're working a full time job and gaming in the off time, you've got to take things pretty seriously. Remember, the pros are getting more playtime than you, playing with better players than you, and they don't have things like school or their 9 to 5 job to worry about. I'm not saying you should quit school or work, I'm just trying to paint a picture of the odds you're up against.
You can counter this disadvantage by treating your burgeoning pro gaming career as a second job. Set a practice schedule up for at least twenty hours a week. That doesn't mean just playing the game either. During a practice you should be playing online against players at your level, or playing solo and learning the maps and mechanics.
At CES 2009 I spoke to Johnathan "Fatal1ty" Wendell, the first pro gamer to make over $100,000 a year gaming. I asked him about his rumored four hour a day practice regiment and he clarified that he practiced in four hour increments for a total of eight hours daily.
It's important to know your weakness and work on it. If you're a great sniper in Modern Warfare, but lousy up close, that weakness should be the focus of a least a part of your training session. Play for a full hour without letting yourself use a sniper rifle and constantly strive to improve.
And remember, it is work. Though you may not need a full blown home office, it's important to have some of the essentials available to you.