I've tried several, but here is my favorite technique. It came from an issue of Quilting Arts magazine a few years ago. To do really artistic dyeing, you need cheap plastic wrap (yep, the kind for food, get the cheapest you can fine), Rit dye---liquid or powder---in several colors, newspaper or a plastic table cover, a microwaveable dish and a microwave. This is easiest with pieces of white fabric a little narrower than the plastic wrap BUT you can lay out pieces of wrap overlapping about an inch, press well so it sticks to itself, and use that. If you have powder dye, mix up a strong solution of each color.
Lay your washed and dried fabric out on the plastic wrap. Starting with the lightest dye color, dribble, brush, spoon, fingerpaint or whatever the dye on the fabric. There is no such thing as too much dye, just do what you like! Repeat with all of the colors that you want to use. Then start at one short end and roll up the fabric with the plastic wrap, like a jelly roll. Be sure it's tight. Then pinch the ends tightly to seal. You have to make an airtight seal, so if it doesn't work out that way, just grab another big piece of wrap and wrap your now-sausage-shape up again to make it airtight.
Put it in your microwave safe dish/plate, coiling it around as you need to to make it fit. Then microwave it....a fat quarter or anything smaller than that takes two minutes and you can guess from that how long to give bigger pieces. Precision isn't that important in this step! Then set the dish out to cool. If you can't wait for it to cool, you WILL burn your fingers on the boiling dye! When it's cool enough to handle, IN THE SINK, unwrap it...the plastic wrap may have to be torn away but that's fine....and then unroll it. Rinse in cold water until the water runs clear. Let dry, and it's now colorfast! You can also do a kind of fake batik with this technique by drawing on the fabric with Elmer's Blue Gel Glue (no other glue, trust me!) and letting it dry, then doing the dyeing as above. That was really what the article was about. The gel glue comes out in the washer after a couple hours soaking in cold water.
I love this technique since Rit is cheap and unlike the other dyes, it lasts and lasts, even after it's mixed.