Measure the height and width of your wall. Sketch it to scale on graph paper so that every 3 inches is equal to 1 square on the graph. Mark to scale the space taken up by any furnishings or other items that are in front of the wall.
Select a group of items that are related in some way. One option is a collection of photographs that are all black-and-white or all mounted on a white mat. Alternately use a collection of plates and platters or decorative baskets. While the items needn't be identical, there should be an underlying theme that ties them together.
Measure each item's height and width. Make a similar shape to scale on another sheet of graph paper. For example, if you have a 12-by-24-inch framed picture, it is represented as 4 by 8 squares on the graph. Write a short word or two inside the shape, so you know which item the drawing represents, just in case you have several of the same size.
Color each shape with the dominant color in the item it represents. This is only necessary if there are a variety of colors in your collection. If they are all the same shade, balancing the colors isn't necessary.
Cut out all the shapes representing your wall-hanging items. Lay them on the first sheet of graph paper that features your wall space to scale.
Play with the shapes and move them around until you find an attractive, balanced arrangement. You can line them all up so it's very symmetrical and even, or you can make it more like a random collage. Consider whether you need more pieces or want to discard some.
Tape or glue down the shapes when you're satisfied with the arrangement. Use the scale diagram as a reference so you can hang your collection on the wall exactly as you've planned.