Here are some background ideas to inspire you to create;
☺♥☺Phone book pages make great backgrounds. They are cheap, plentiful, and the pages are lightweight, so they lend themselves to many mixed-media art applications. Be sure when you use phone book pages as backgrounds that you apply enough other media on top to obscure the names. Old book pages work well, too.
☺♥☺Make textured paint backgrounds. Using acrylic paint or watercolors, apply a wash of two to three colors to your paper or canvas. Then, tilt the substrate this way and that to allow the paint to drip and make rivulets. You could also dab the paint with a wadded paper towel or bubble wrap, or lay crumpled plastic wrap on the paint, let it dry, and then remove the plastic for a mottled effect.
☺♥☺Use resist techniques. Lay down shapes or writing on your substrate using a paintbrush and gesso, a hard graphite pencil, liquid graphite, a stylus, or even a wax crayon. Then paint over your substrate. The paint will resist the areas where the shapes or writing exist, creating a background with depth.
☺♥☺Maps and brochures make terrific mixed-media art backgrounds as they are full of lines, colors, and numbers. Of course, you will want to omit or obscure any material protected by copyright.
☺♥☺Another art technique you can use to make backgrounds is to reuse paper or “failed” artwork as a substrate. What could be faster than starting with a material that is already a perfect background?
☺♥☺Recycling art is a quick way to start a new piece. I like to use gelatin monoprints that don't stand on their own or that suffer from poor color combinations or smudged images.
”Beginning with audacity is a very great part of the art of painting.” -- Winston Churchill