The ur-rule for social interaction is pretty simple, actually (in form at least):

Do whatever will raise your status. Avoid that which will lower your status.

(Edit: See wedrified's more nuanced explanation below)

Confidence is simply a proxy for a certain class of high-status behaviors. PART of that is not displaying concern at how your behavior is interpreted (because if you're worrying about your status, you're obviously low-status), but if your behavior isn't in the ballpark of "proper" already this will backfire (unless you're so high status that you can re-define what proper behavior is, or at least make people question their knowledge of it).

Of course, if you've got a busted status processor - and I suspect social awkwardness/social anxiety are essentially cases of faulty status processors - this is entirely unhelpful. But it does serve as a framework for organizing all the social advice you get, and will help give you an idea of what a proper answer looks like.