generally, make highpoly, make lowpoly, UV lowpoly, make a bake, see that it sucks, revise lowpoly, redo uvs, bake again, fuck with your cage, bake again.

but that's just for single things.

MOST of the time, (for environment art at least) you'll be mapping existing textures to new meshes which they were not made for, and you're just going to have to make it work anyway.