It was pointed out to me that I didn't include a tutorial for Kool-aid dyeing yarn. I guess I just assumed that everyone else trolled Craftster, and all the other craft sites as much as I do. Oops. Here's a link to a good yarn dyeing tutorial at Knitty.
Here are a few tips from me:
Remember your color wheel. If you dye the yarn pink and blue, it's going to be purple where the dye blends. That should be pretty. If you dye the yarn red and green, it's going to be brownish where the colors meet. That may or may not be pretty.
Try not to wring or squeeze the yarn any more than you have to. You might felt it.
Don't rinse your hot yarn with cool water. You might felt it.
If you are painting yarn, be sure the dye is fully saturating the yarn. If it doesn't, you'll end up with patchy looking color.
You can always overdye yarn, if you aren't happy with the results. The other day, I dyed a pink and blue batch. (I've done the same color combo several times.) This particular batch wasn't as bright as usual, so I overdyed the the whole hank with strawberry Kool-aid. The resulting yarn was actually really pretty. Hot pink where the pastel pink had been, and purple where the pale blue had been.