a) By far the most important Q/A technique is telling the truth about relevant Q/A issues in a way that can be understood by your audience.
b) Of course, you must first be able to know what is the truth, and that requires observation skills of a high degree.
c) And, too, you must be able to know which truths are relevant. For that you must understand the processes practiced to produc the products whose quality you are supposed to be assuring.(see the Quality Software Series)
All specific techniques are dependent on these underlying techniques. If you lack a, b, or c, you will not be able to perform other techniques well.
If you wish to learn more about any of these techniques, or others, I’ve written many books on these subjects, not just the ones shown here. For a list of these books, see my author page on Leanpub.com