Like the poll says.
I try to plan 3 subs ahead to get a +1 game played stat and possible a few skill points for new transfers/ fast learners.
In tough matches I'll also plan 3 subs, usually to swap in "fresh legs" in attack or central defence positions.
Usually I make subs 60-75' in, or start at halftime if I've got a lead and can replace a non-learning vet for a younger player, same position.
PS- I'm sure I missed good poll options, feel free to discuss your tactics.