Hi, I started only back in December. Best advice is to go back and read all of the information in the new mystery shopper page. There is some pretty detailed information in there on how to get started. After you sign up with a few of the suggested companies, read, read and read some more. This group is a great source of information.
then pick a shop that interests you and seems easy and try it out. Start small, work your way up to bigger things.