Any tips on starting an affiliate program?

Hey,

It's time to expand my business! I'm about to start an affiliate program and in the process of getting the legal agreement from a lawyer. It's my first time doing anything like this and I'd be happy to hear if you guys have any tips on things I should do or avoid doing.

I'm thinking things like shouldn't I set some sort of time limit for the agreement or do I keep paying the affiliates until the end of time?

Thanks a lot!