Understand the Theory

Of course you have to understand a theory before you can use it, support it, and all the other things.
However, there are varying degrees of understanding.
You can really dig into the theory as an entry to the domain.
This forces you to enrich your cognitive map.
Theories are just particularly important parts of that cognitive map.
You can do this by reading, thinking, experimenting, and talking to other people.
Really famous academics (usually )absolutely love it when you ask a question about their theory that no one has asked before.
If there are equations, you need to work through them.
If there are competing theories, you need to understand them, and the differences.