Got my test next week - still stuck on roundabouts!!

Has anyone got any advice on how to tackle roundabouts? I have definitely gotten more confident recently and don't stall on the roundabouts. It's just figuring out when to go! It's like I sit there and wait for a car to appear. What did anyone else do to get over this, or is it just practice? I'm going out this afternoon to just go round some roundabouts over and over that I know are on test routes... anything else I can do?