(a friend asked. this is what i got to say.)
OK. Here goes.
0. I'm not sure how long you've been illustrating professionally for, all that stuff, so some of the stuff I'll say will be bleedin' obvious. forgive me.
1. know your stuff. know how print works, colour and black and white process, how to supply art for different media, image resolution, inkweight, know your software. obvious really, but if you want to be a pro, be professional.
2. being in the sticks means nothing these days. G+ especially has changed EVERYTHING. so use it. you now have direct access to ANY rpg producer who's on G+ and sees your work. publish your latest art piece at least once a week if not every three days so people are aware of who you are and what you do; if people like what they see they'll recommend you.
3. being on G+ has its negatives. anyone can see what you say, so don't be a dick. be excellent, be funny, be natural (people will see through any persona and it's a bitch to maintain), but avoid getting into controversial fights online. waste of time anyway.
4. answer all communications with employers and potential employers promptly and precisely and honestly. Say no if you can't do a job rather than take something on then fail to deliver. And if you're going to fail, let your employer know asap. They'll be understanding if you're upfront and honest.
5. look for opportunities to bolster your reputation. don't work for free, but if you do anyway, make sure it's worth your while. Santicore was a chance blessing that I was in a good opportunity to run with and it worked.
6. get it in writing, if you can; if you want to fly casual, be zen when things fall apart and not in your favour. use gmail chat to communicate real time discussions about stuff, you can go back and search them later (I've done this a few times when costs have been queried. it helps alot).
7. be good with money, or if you know you're shit find someone who is. the tax man will come, sooner or later. deal with it on your own terms.
8. there will always be better artists than you. In my circle of friends in RL I'm the drawing dude. but I'll go to conceptart.org and weep at how phenomenal they are and I'm not. So I figured if I can't be awesome, be unique. develop a signature style that's striking, is easily associated with you, and doesn't take forever to execute. if it's good, people will come to you looking for your style. if it's the same as everything else out there, they'll go for whoever's cheap and fast; cheap and fast is the least successful way for you to produce work you're proud of, and if you're not proud of your work, you shouldn't be wasting your time doing it. life is too short and brutal for such waste.
9. blog it. have a readily available gallery of your work. people will want to see it, and make sure it's interface isn't too fancy. it's your work they're here to see, not the website, and if you can't access it with one link from an iphone, it's not working.
10. work out a reasonable hourly rate in reverse. weekly budget reqd divided by number of billable hours, and don't forget tax and super and all that. don't drop that rate unless you're starving. assuming you've been to college, studied hard, and have been working for a few years, you should to be treated with the same respect as anyone else in any other profession. people will take you for a ride if you let them. if you're set on being a professional illustrator for the rest of your life, do it with the respect you deserve.
11. stop looking at the computer from time to time. get out and get some sunshine. it's only work.
that's all I got.