Upwind in a drifter, you need lots of downhaul to let the sail twist and flatten. Then centre the traveller, and pull the mainsheet in but only so much that the sail can still twist off. Then just steer to the tell-tales.

As little puffs of wind come by you can pull tension on the mainsheet so long as some twist stays in the sail, but make sure you let it off again as soon as the puff passes.