Start with a phone call....non confrontional !!!...
ask how he ( or she) is doing?..be concerned,..then say the reason you called is to "resolve the bill".....
Be nice. hear thier excuses.....make faces,....roll eyes......but be nice.
2.,,, if no money....send letter.......be nice but firm.....let another not involved person read letter.....before mailing it to make sure your anger does not come out.
3. if he is nasty at any point.....let him stew, just be nice and firm....anger on your part at any point, will make him feel jjustified in not paying....
4. make a deal....can fit any where in.,,,but make sure it is only good for say,.. 15 days.....and if he puts it in writing and he signs it....you don't have to sign it remember it is his offer.....not yours....and it is only good for a few days........as some deals can come back to bite you in the behind...so make sure it is his offer...on paper....and not your offer to cut a deal on paper....!
5. if nice firm pressure fails...and you know he is not going to pay...collection....if he wrote a bad check file criminal charges...if he signed paperwork....small claims court....and liens on actual items,..equipment,..or property....
good luck.....be nice....but firm.....and no cussing!