Asking for a deposit is a really smart idea, especially for project-based work. As a freelance writer/editor I've never tried it before but if I'm contracting for, say, 5 blog posts to be written on a pay-per-post basis I might send the initial invoice after I've completed the first assignment instead of all five (they all say "payment due within 30 days of receipt"). I wouldn't do this for a new client but for the ones I have in mind I think it might work. Then when they're "late" they're actually on time - haha!
