Sign up for as many as you can to start with. I wish I had saved a standard writing sample of an experience, retail, and dining. I know some companies request a writing sample in an expanded application process. It goes faster if you can do an easy copy and paste.
There are different reporting platforms out there, so as you begin, do not take on too many different assignments in one day until you are used to them. Remember, if some shops are repeated frequently, the first time you do one there is always a learning curve--gas stations, grocery, certain banking shops, other retail--but if you find the ones you like, they become second nature and convenient to do in your daily routine, reporting included. I enjoy the virtually free oil change shops. The reporting is always easy for the reimbursement you get and the time it takes to execute.