I'd start by looking at the geometries of bikes on various manufacturer's web sites. Surly, for example, lists the geometries of all of their bikes. Sheldon Brown has scanned old Bridgestone catalogs where you can see what Grant Peterson was up to with road, mountain, and hybrid geometries. Then think about the bike or bikes that you own, and maybe try to ride some with different geometries. It will all start coming together, but it's a huge and contentious subject and there is no one place to find the right answer. Beware of anyone claiming to know anything about the subject, and let the existing bikes and numbers speak for themselves.