I decided to try out a bunch of stuff I've been wondering about and so I thought you like to see the results I've collected so far:
Since up until recently I've only worked in altered books, I chose a cast off hard back to try all of my techniques in. I realize my handwriting is terrible, so I will translate.
I placed a stencil to the paper and used the spatula (picture above) to spread an even layer of matte gel medium. The top bird was left smooth while the bottom bird's gel medium was disturbed by using the width of the spatula to press into and the pull up the gel for texture. Both were painted over with acrylics afterwards. The smudge of paint on the side shows the true color unaffected by the gel.
Same spatula, different technique. At the top, a thick layer of matte gel medium was spread onto the page and the I used the pointed tip to draw into the gel. The bottom corner was the same texturizing technique I used on the bird in the last photo to create a spackled look. These were my first experiences with any gel medium and I think it would look better to mix the paint with it first rather than painting it afterwards, it looks muddy here.
Here I experimented with a rubbing alcohol resist, the page was painted with watercolor and then splattered with the alcohol. The watercolor recedes and creates a speckled look.