I read in a book about racing to split the hill into thirds.
Go into the first third slightly under geared so you are properly spinning, then as the hill ramps up you sort of settle into it. Once this has happened start to wind it up through the second third and then give it the beans to just after the summit in the last third.
I've used it on smaller hills and like it, although it made me puke the other week.
For bigger hills, I just find a gear that works, start spinning and try and keep a regular rhythm. Maybe when I'm better at it you can split those into thirds, dunno