There's a book on High/Low Split Poker by Ray Zee (I think), which is pretty interesting, too, covering both 7 Card Stud H/L and Omaha H/L. It discusses more about when you should or shouldn't limit the field and so on, and explains things pretty well.
You could do worse than to look up the Hutchison point counting system, too, as that gives you a decent basis for valuing starting hands.