Disclaimer: If you're asking how to play poker for a living, you've already missed an important question, namely WHETHER to play poker for a living. If you're just starting to build a bankroll, it's not time to make that kind of decision yet. What follows is my attempt at an answer assuming you've done your due diligence on the question of WHETHER to play poker as a source of income. This is not an assumption to be taken lightly. That said:
I've made money part time playing poker. I offset the cost of my wife's anniversary present last year with poker winnings(an old motorcycle beyond the means of my summer job flipping burgers), and paid for part of Christmas this year by cleaning out my pokerstars account. I'm not a pro, and am really only a slight-above-average poker player with enough discipline to lay down when I have the worst of it and push with the best of it, accepting that I will sometimes get outdrawn. I only had time to play high-stakes ($1/2 NLH-it's high to me, as a college student, lol) over the summer, and stuck to very low stakes online (in the 2nl to 5nl range), so my winnings were about $1500 last year, the vast majority of which came from my summer nights at the dog track playing live. However, I can tell you a few things. Part of this is based on mistakes I've made, hoping you can avoid some of the pitfalls I've discovered. All of it is written on the assumption that you're already a strong player. If you're not, then my advice is simply to play poker with money you would have spent at the movies/bar and enjoy your wins when they come. If you're a +EV player, though, your biggest skill is money management. In no particular order:
1. Never clean out your bankroll. It's hard as hell to start back up again. Not being sufficiently bankrolled, I've left the live game, and am just grinding the [expletive] out of low-stakes NLH tables to try to rebuild a bankroll. In fact, if it can be helped, never spend your bankroll. On anything. Ever.
2. Have a large bankroll. Maybe this should have been #1, but I said "in no particular order" for a reason.

Someone else mentioned $4k as a good $1/2 NLH bankroll. While the exact number varies depending on what you read, that's probably a decent bare minimum. And remember that this isn't cash on hand; this is the bankroll. This is venture capital that won't be spent on anything but chips for a little while.
3. Have a couple months' savings socked away, or since you said part-time, be able to meet all your obligations with your other job, even if you have a poor month at the tables. One way to do this is to have a good job. The other way to do it is to keep your obligations low. If you're serious about this and have a car on which you still owe a payment, try to get out from under that and buy a good beater if feasible. If you're carrying any other debts, the same idea applies. Go Dave Ramsey on that ****. Even if the poker thing doesn't work out, it'll make the next fifty years a lot less stressful.
4. See a LOT of hands. And I mean A LOT. Even if it doesn't feel like it, if you're a +EV player, you're essentially getting paid by the hour. Sure, some hours you make $100, and some hours you lose $50, but over the long haul, you're still making $25/hr. As such....
5. Don't forget about online poker. Online, you can see almost twice as many hands per hour as in a live game, and you can play multiple tables. I'm not the multitabling psycho some of the folks here are, but I can play six tables at a time relatively comfortably. By doing that, I'm seeing nearly 12 times the number of hands per hour online that I see in a B&M card room. This insulates me from variance, since I'm (hopefully) taking the good end of 12 different gambles over a given time period rather than one. I can also buy in at lower dollar amounts but still have a similar win rate. You might find that you can make more playing six tables with a 25-cent big blind that you can playing one live table with a $2 big blind.
6. Be prepared for swings. If you've worked in sales, you know about the feast-or-famine lifestyle. Poker is that much worse. Even the best pros go through brutal stretches where they lose time after time, despite playing "correctly" the vast majority of the time. I discovered that I can't go to the card room, lose $400, and come home and hug my wife just as happily as if I'd won $100 (about what I'd make on average playing 8 hours at $12.50/hr). If this describes you, and you like having friends, keep poker as a profitable hobby rather than a part-time job. Similarly, I have in the past foolishly felt that just because I won last week, I'd win again the next week, and ::gasp:: spent the money in my pocket. I don't know whether the upswings or downswings hurt more, but both can bite you if you're not careful.
7. Keep careful records. This may be important for your legal well-being as well as your poker career. You need to know how much you're actually making and when you're making your money. Last summer, I was busting my tail to get out to the card room early in the day to get in as many hours as possible. After looking over my records, though, I found that I was only really making money in my night sessions. After that, I picked up more day shifts flipping burgers. When I got off, I'd go home, shower, enjoy a late-afternoon or early-evening meal with the Mrs., and head off. I was playing five hours instead of 8-12 hours, but making about the same money. It would be misleading to say I gave myself a raise (I played fewer hours, but made about the same money), but I made a little more because I picked up a couple of extra day shifts at minimum wage. Also, if you're paying your bills with poker winnings, it's probably time to consider filing that on your income tax return. In the interest of full disclosure, I haven't done this, so I'm not exactly practicing what I preach, but if I get to the point of cashing out monthly, it will become necessary.
Well, that's not everything (not even close, in fact), but that should at least give you an idea what you're getting yourself into. Assuming you're +EV, the crucial skill isn't really poker ability; it's money management. I hope this helps, and one way or the other, best of luck.