Uh so this is not a tutorial, 'cause I'm pretty sure you all know what a stencil is, but this are a couple of photos of how I made some pretty backgrounds for my drawings.
I used very cheap tools like an old sponge, acrylic paint, an used toothbrush and a paper cake doily. (and newspapers, gloves and an apron to not make a mess of me or my room)
Mmh I hope this can give you some inspiration! if you have question just ask!
Stay groovy ;-)