http://www.thedailysail.com/ism/article ... enDocument
http://www.thedailysail.com/ism/article ... ent&Page=1
These articles are pretty good.
As well you may try looking up some Nacra F18 tuning guides and tips...much of it is pretty similar.
As far as downhaul and mast rotation.. depends on how you're sailing. If you're not going as fast as you'd like you may try easing up on the downhaul and letting out the rotator a little bit. General tip is for full power sail with the rotator pointing at the shroud, easing it out a bit more in lighter conditions and vice-versa.
Your downhaul will generally get tighter the heavier the wind. If your sailing high and still having trouble keeping the hull somewhat flat then you may want to try (among many other things) tightening the downhaul.
These are some things you'll just have to play with in different conditions to see what works best with your rigging. If your still not feeling like you're sailing right then maybe try playing with your mast or spreader rakes or your tension.