An inexpensive way to make art for your walls is with fabric. You can screw together a wooden frame either by using canvass stretchers (glue the corners) or 1 x 1 pieces of wood. You can then stretch a fabric over that and staple it to the back. You can also attach a piece of light plywood or MDF to the frame, upholster that and then attach a picture hanger to the center to make an already framed photo or picture seem more important and take up more space on the wall.

You can also purchase already made canvass attached to a frame (Big Lots has the cheapest ones) and make a collage by decoupaging items to the canvass. You can make a scrapbook of a trip by attaching museum tickets, postcards, and other momentos to fill the canvass.

Think out of the box, too. I have a collection of Japanese and Chinese silk kimonos and jackets hanging on drapery rods on a 2 storey wall in my living room. Maybe you have something that normally isn't hung on a wall, a collection perhaps, that would be a unique and dynamic displaly.