a Lifesaver is a kind of shoulder check, its the one you do whenever you are crossing the path of traffic. So when youre turning right for example or just before you commit to the u turn. As for other shoulder checks, you should always be doing them when youre changing your position on the road whether it be inside your lane to pass parked cars or to go round a bus on the opposite side of the road. Mirrors should be checked before the shoulder check. Sof if youre coming up to a parked car and need to move out, youd check mirror, check shoulder, move out then check mirror, check shoulder, move in. As for which shoulder to check, you need to check the direction in which youre moving, so moving right, then its right shoulder and vice versa. If youre having lessons then ask youre instructor as well Im sure someone will pick me up on anything i have forgotten to mention!