The basic adjustment bit is easy:
Loosen off the "second" shoe (the one that isn't directly attached to the cable);
Tighten the "main" shoe up until it is just rubbing;
Then tighten the second shoe until it is also just rubbing;
Back them both off and set the cable tension.
There are other tricks like tightening the axle with the brakes held on hard, and filing the shoes to match the drum, but that's the basics.