Just a suggestion - get certified at MSPA (Mystery Shoppers Professional Association). Also, Jobslinger.com has a free trial of their services which targets companies using the Sassie service. Both websites have invaluable information for you. A lot of what you'll learn comes from trial and error. I've been doing this for almost 15 years and I'm still learning new things all the time. My biggest piece of advice is to just enjoy yourself. If it gets to be too stressful, you're either doing too much or working for the wrong companies. Sign up for all of them and you'll figure out which ones are the best fit for you.
Maintain an attitude of gratitude!