I draw up a simple contract with regular payments via paypal. I only ever give a client my paypal email, never any other bank or payment details. I do small chunks of work so if a payment didn't go through I wouldn't have wasted a huge amount of time. I also state in the contract that I retain copyright so if I've done the work and payment hasn't been made I can legally sell my work elsewhere (legally - although practically this wouldn't necessarily be possible if it's a very specific brief). So far, I've received prompt payment from everyone I've worked with, but I'm very aware that things can go wrong so just try to protect myself as best I can. I also assess each job carefully. I had a request recently that sounded totally unprofessional and the site I was supposed to write for looked a bit scammy and had no proper contact details (ie no physical address or phone no, just a contact form), I politely declined.