Wow - this is interesting. The technique I could never get down was the one where you use egg shells - can't really recall the steps but it was icky looking. Also, chalk and blender pen is not good for me either.
here are some hints that might help:
Shrinkplastic - try using the oven technique - can't recall the temp, but you cover a cookie sheet with foil and bake.
Bleach - I get best results with a gel bleach pen
Crayon Resists - I have to put down a lot of crayon to make mine look good
Watercolor Spritz - color stamp twice with marker, hold stamp at arms lenghth and spray with a fine mist (not the mister you use with an iron). Let the water run around a little - it should not have a lot of water. If you get muddy colors - it the color choices that you put next to each other.
Clean image on watercolor paper - try using Bristol watercolor paper - it has a smooth finish
Sponging and brayering takes practice to learn the feel of how hard to press. It took me some time but I do a decent job.