We testers set a great store to test design techniques. TMap Next dedicates about 17% of the whole book. "Foundations of software testing" by Graham et al., dedicates about 20% of its content to explaining the functioning of different techniques. Strangely enough, how to select a technique is hardly discussed. In my opinion that is a shame, because selecting the right test technique is important for the efficiency of testing. My experience is that many testers find it difficult to select the right techniques.
Selecting the techniques you are going to use is a careful process. Selecting the wrong technique may cost you a lot of time without finding many errors or useful information. Failing to select the right technique may lead to mayor defects not being found. By using the right techniques, the tester executes the right tests and is accountable for his actions and the quality of his advice. Since the techniques define the tests that are executed, they also determine the information that can be given to the stakeholders.
Many times test techniques are applied because the tester is familiar with them and the test base supports the technique. I'll explain the decision model from my book, and will inverse the problem. We do not use techniques because we can, but because they help us to provide the right information. Unlike many methods we start with the errors and select the techniques that help finding them.