If you're confident you can get away from the lights quickly, position yourself directly in front of the first car. (There are places on my regular commuting route where I do this and stay in front of the cars rather than move to the left. I'm happy to do this because I know I'll only have the same problem again 100 yards up the road if I let them pass. Some of them don't like it, but that's their problem. Letting them overtake me wouldn't actually help them get where they're going any quicker.)
Otherwise, wait behind and to the right of the front car,* and as you pull away, filter in ahead of the second car (much like Mr B and Basil describe).
Sometimes, if the road really is clear and the cars are quick out of the blocks, I'll stay out in the middle and wave cars through on the inside until there's a gap for me to filter back across.
d.
[*edit: or, as others have said, the second or third or fourth car, depending on the situation]