I think you brush upon a quite important point here: good conversation is less about being good at conversation and more about not being bad at it. People will talk quite happily with someone who is utterly boring, so long as it's not for too long and they've got nothing better to do.

People are only really put off a conversation when a person does something odd.

Prime among these are non-sequiturs, unusually extreme opinions (especially about topics people normally don't have extreme opinions about), and discussing topics which are generally understood as not being suitable for general conversation (such as topics which are invasive/personal, obscure, or too academic for the context - it's fine to talk intellectually in the appropriate place, but not to strangers at a bar/club).