Honestly, from someone who had 0 experience with it, the secret is, looking at what the BigFix team created in their fixlets and relevance and bending it to your will. It really just takes some time to get used to but, soon enough, you’ll be fluent in relevance because, to me, it’s just like asking the computer questions and it giving you the answer. Here is some links to hang onto.
Inspector Reference - A collection of all the inspectors that can be used for analysis
Action Reference - A collection of the inspectors and their use for Action scripting
With these two references it all comes down to what you really want to know about your environment and you just start creating. Good luck!