There're a few comprehensive write-ups and guides out on the net - the ones I'm most familiar with are at granturismobynumbers.com. There's a large guide written by Gasman and a couple of tuning threads that go into depth on various aspects of dialing a car in.
Have a look and see what you think.
Also, try some of these out; they're sites which contain technical information (some of which may be more mathematical and detailed than you want but worth a look anyhow):