Firstly, you need to choose items that you will be putting up on the wall. Don't worry about the size too much, as long as nothing looks odd and out of place. You must also keep your overall theme in mind before selecting decoration pieces for your wall.
Consider hanging a piece of fabric, rug or tapestry on the wall as the main decorative object and then surrounding it with smaller objects. To keep the smaller items from giving a scattered look, keep them as close as possible to the main decorative item, in this case the piece of fabric, rug or tapestry.
If you are alright working with paint, painting a mural on the wall would be a very good option. The mural can be anything, from an intricately drawn landscape to a simple pattern made by painting geometric shapes.
For a more artistic touch, you might want to hang a piece of art or mirror on the wall. The best place for a painting or a mirror is right above a sofa, desk or headboard positioned against that wall. You can experiment with the height of the piece you put up to find out the best position.
For visual appeal as well as functionality, consider attaching one large shelf or a number of small shelving units onto the wall. Make sure that the shelves are attached at an appropriate height above the floor and after you have attached them, give the room a final look to make sure that the shelves complement the rest of the furniture in the room.
You might want to display some of your favourite objects in the shelves hung on the wall. Position the shelves in such a way that they look like a group. Make sure that the items you display in these boxes are clean and go with the overall appearance of the room. You can also put simple photo frames with family photos in them.