Theres a lot of ways to make textures: acrylics, watercolors, inks, gouche (all this over a lot of supports like bond, canvas, et al), photos of walls, concrete, etcetera; but this time I wish to show you a very easy and cheap way to make a texture for your illustrations.
1.- Basics: water, coffe, masking tape, blank paper (or other soft color) and…
2.- …spray bottle. First step: Mix the coffee with the water and spill it in the spray bottle.
3.- Spray the water-cofee mix all over the paper.
4.- Put the wet paper under the sun and over a real dirty surface. By the way, my english sucks… but you understand, right?
5.- Here, you can see the dry paper after his first bath. This can work like a smooth texture, but I prefer to experiment a little more…
6.- …Ta-daaaa!! Look better after severals baths later. Scan the paper at 400 or 600 dpi, save it… and thats all, enjoy your new texture!
Please, dont take this like a tutorial, I just want to show you part of the process which I follow in some works, but theres infinities ways to obtain the same goal.