If you're on a larger roundabout (2 or more lanes) and are going right at the roundabout you'd need to initially position yourself in the right lane. At the penultimate exit to yours you should "mirror, signal, shoulder check left" and move across to the left lane ready for the exit (move left early to "shut that gap off" so no one can undertake, making you go round again). As you've positioned left, you've left a gap to your right where another vehicle can (and has done on me!) try to rush through and take the same exit as you but cut across you just as you're turning in. So giving a final quick right lifesaver will let you know if anyone's trying to do that. EDIT: on a smaller, single lane roundabout only a left lifesaver is required, because you're all the way across to the right until you need to come off anyway. I was taught to give a right shoulder check for the reasons above. I do it so I leave myself plenty of time to re-assess my exit (which I had already checked before doing the right shoulder check.)