Note that sometimes pronouns 'point forward', as in When she had sat down at her desk, Mary started writing the letter.
Note things like He's very good at maths, is Jim. (Colloquial)
A few pronouns are indefinite and have no antecedent:
One should not do that (assuming that one is not a pompous way of saying I).
You must be careful (assuming that you means people in general).
They are digging up the road (where they is used for some unspecified, remote authority).