I think that Thorman's reccomendation is a very good place to start. I read a bunch of stuff before positioning mine some time ago, then followed this rule and the ultimate position was very close. Plus, many of the calculations presented seem good in theory but not practical unless you have a fully dedicated room with only audio equipment and a listening chair!
You will have to make adjustments wherever you start. Just try to absorb the results of a move with a more than a few listenings, lest you get caought up in making quick, multiple back and forth moves, not really sure if you've improved things.