Hmmm, there are a lot of different methods and such people have for keeping their wigs nice. I'll just post my own personal preference on how to work with things.
Defiantly get some wig heads. Styrofoam ones a great if you are going to be styling, straightening or washing a wig. I recently got some little plastic ones too that are more stylish and aren't as ugly. I've heard they are better for some reason, I'm not sure why. Both are around the same price though.
If you don't have the money to invest in wig heads, your best friends are plastic bags! Save the bags that your wigs come in! They are really sturdy and great for transporting wigs. If you threw them away though, you can just use ziplocs.
If you are storing long wigs the best way to keep them looking nice and to avoid tangles is to put the hair in a loose braid and either a. wrap it around the base of the wig head or b. Turn your wig inside out and tuck the braid inside it before sticking it in a ziploc.
Short wigs are a little easier, just leave 'em be if they are on a wig head or just turn them inside out before sticking them in a plastic bag.
ALWAYS STORE HEAVILY STYLED WIGS ON WIG HEADS.
Buy a wig brush. They may not seem likes the help much but I recently bought one and OH LAWDY, IT'S SO NICE. Doesn't pull out as many fibers as a comb or brush would and it's got nice little metal bits in it...
If I have a wig with little styling (like just a little hairspray or something) I like to wash them after a con. The method that Cassiopeia suggested is the best. I usually do that and then put one of my wig heads on a broom and take it in the shower with me. I'll brush it out in there since it seems a little easier. I also put just a LITTLE bit of conditioner on my wigs. It helps take tangles out wig and makes them smell all nice and pretty.
And that's really it. Hope that helps.