Step out of the water, lather up hands, scrub, then back into the water to rinse. Face, then hair, the upper body then lower body - with a good spray of the undercarriage (shower heads are supposed to be removeable, not stuck to the wall).

It's a pet hate of mine that people often miss the step of rinsing when cleaning. The whole point is that the soap picks up the muck, then rinsing it removes it. This is a particular problem with dishes, where people leave (sometimes very dirty) dishwater on the plate to drip dry, with much of the residue remaining. My dishes fucking sparkle, and that's because I rinse them clean.

In contrast, with showers I think some people lather up in the water, which dilutes and rinses the soap away before it even cleans anything.