Mystery shopping is a great idea of a fun job if you enjoy shopping a lot. However it takes time and effort and observing your surroundings while not making it obvious that you're making it known to evaluate the store.
First things first-- apply to many mystery shopping job as possible. There always a chance there is not a opening right away when signing for only one or two. Besides the more you apply to,the more money you make.
Step2
Keep a watchful eye. Remember the keyword is 'mystery' shopper so you want to keep a low profile of yourself. Have a clear memory and remember every detail that is going on around you in a store. Is the employees polite? Were the helpful? Did it take forever to purchase your item? Is the store clean? These are the questions you need to ask.
Step3
Well written evaluation. Write a detailed report describing your experience in the store. The informative your report is, you will find yourself with another assignment and earning money quickly.
Step4
Be reliable. Just because it's an independent contractor position doesn't mean you should abuse your freedom. Just like a job onsite, prove yourself to be dependable and available to accept an assignment. Constantly canceling because you just didn't feel like working on that day is a turn off and a possibility that someone else will take your place.
Step5
Gaining experience. After you got the hang on doing a good job as a mystery shopper, don't be afraid to reject an assignment that is low priced.
Tips & Warnings
Have fun while shopping.
Never pay for a fee. If any fee is 'required' report the business to Better Business Bureau.