Mixed media art includes many types of crafts and arts, which include collage, handmade cards, altered objects, art journalism and book making. Scrap booking can also fall into this category since you are using photos and paper, which are considered to be mixed media.
Everyone can create mixed media regardless of his/her artist skill level and the materials that one has at hand. In order to get started with mixed media art, the only thing that you need to have is the desire to come up with something. You then need to have a base or substrate, which could be a good piece or cardboard, paper, a cereal box, sketchbook or anything else that you have on hand.
You should then get something that you will use to stick the substrate with and glue sticks are a good example. You can stick pictures, colored papers or anything else that you find attractive. This is what is considered as collage in the mixed media art genre. If you are interested in painting or drawing, you need something that will allow you to make marks.
This could be a pencil, marker, crayon or pastel. You can use these items in different ways in order to achieve various effects. You can use them separately or in combination. Since you are aiming for mixed media, you can make it completely mixed by using a large number of different tools.