Reflecting on seminar talks and job market talks especially, I think one key sign of a successful talk is if you're having a genuine debate about whether the ideas in the paper are wrong or not. Unsuccessful talks never communicate the ideas well enough for that debate to happen.

The main reason for failure on this front is that the fear of being told you're wrong and your ideas are bad prevents you from really, truly *wanting* to communicate them as clearly as possible.

If you want to give good talks you have to learn to love it when people start offering alternative explanations for what you're showing them. (1) they're engaging with you! (2) they understand your idea/findings well enough that they feel capable of interpreting it!

You also have to learn to staunchly defend your interpretation and your explanation. Presumably you have a reason for why you believe the things you're telling people. Just share it with them plainly.