I prefer fixed price projects on milestones basis. Highly recommend an initial feasibility study, this avoids further bad surprises.
Expect from the client clear and complete specification in plain English (usual words, not in technical slang). You must tell me only what to do, I will choose my tools!
Do not take projects based on phantasmagorias like magic winning formula finding, universal knowledge base or chat robot building, artificial superintelligence nursing, etc. The Internet is plenty of ignorants or charlatans who will gladly promise you such things :).
Also, to be clear from the beginning, do not accept spamming or privacy invading application building jobs (like contact or emails grabbing, captcha eluding, etc), will not look for particular persons, accounts or profiles, nor I will crack webpages, codes or files. Apply to the NSA with these jobs :). For me, you must provide legal login credentials for any private web page or database you need to scrap.
For all my works I provide unlimited and free email & Skype support and lifetime bug fixes.