In addition to the packing tips on our web site, I can offer this, which I copied from a message I previously posted to TheTravelzine on this subject:

One thing I have found really helpful is packing like things together (for example T shirts) in Ziplock storage bags - or the zippered bags, in which new pillowcases are sold - and then SITTING ON THE BAG to get all the air out before zipping it completely shut. The stuff stays great - wrinkle free - and I can get lots more in my suitcase that way. Plus, it's very easy to find what you're looking for without messing up everything else in the case. Just about the only thing that I don't pack in plastic is the extra pair of jeans, which I prefer across the top with as few folds as possible.

Hope that helps, Linda in Toronto http://www.thetravelzine.com/friend.htm