Do you roll or fold your clothes? Make use of that expandable suitcase feature? Do you stuff your shoes? What about those bags that you can use to vacuum pack your clothes? All of these ideas are what float around the travel sites for suggestions on saving space in your suitcase.
I'm still not sure if rolling or folding your clothes is best. Some say that rolling them keeps the wrinkles to a minimum but a lot depends upon how good you are at rolling them. At least if they're rolled, when the suitcase is on its side, the clothes don't shift like they do when folded creating more wrinkles. I do roll a lot of things like bathing suits and items that I can stuff down in between my folded clothes to keep them from shifting.
Definitely stuff those shoes with other things. Mostly I do this with socks. After all, they're going to go in those shoes eventually anyway. Other small items can slip inside as well just be sure that if you put liquids or gels in them you use a plastic baggie.
I've often wondered about those bags that you can suck all the air out of to pack bulky clothes in less space. Trouble is, where would you get a vacuum when you're traveling? The same people do make travel bags that don't require a vacuum. They would work on large items but I find that even ziploc bags help just as well with smaller items. You can squeeze a lot of air out and make them compact.
Probably the best method to packing doesn't even involve the actual stuffing of the suitcase. Lay out all the things you think you will need. Then reduce them by one-third. We always tend to take more than we need and most of the world does have a laundry or at least a sink to rinse things out.