I love the look of old book papers...or printed leather...and I think this technique gives me a feel of that with just a couple of steps.
First begin by covering your substrate with torn pieces of masking tape. Overlap them at odd angles for the best results...
Next brush a thin layer of mod podge over the surface and let it dry.
Finally, create a tinted glaze by adding water to acrylic paint. If you want it to stain darker use less water...the lighter you want it -- use more. Brush the glaze over your background and let it stand for a few moments, then use a paper towel to wipe it off. Repeat to add depth...and maybe even change the color of the glaze to give it even greater depth.
It's as easy as that.