My preferred method for motivating players in a new campaign is:
- Ask players to create PC's with motivations for adventuring. Actually, I don't literally ask, because I don't have to. They always do.
- Start campaign off with cliches, wild coincidences, and other assorted cheap tricks that get their PC's involved in the action. Any action will do.
- Keep making up new and hopefully exciting situations in response to where they go, what they do, and whatever they show interest in.