Instead of drawing lines on the wall, using a level, etc., etc. I use computer paper or notebook paper. If needed, just cut down to the size of the frame you will be hanging. Mine were approximately 8x10 and so I left them.
You can mark on the pieces of paper exactly where the nail needs to go. This is especially helpful if the hangy part of the frame is more in the middle than at the top. Then tape the papers to the wall using whatever tape you have handy. Scotch tape works on my walls but more textured walls might need something stronger.
And you're done! Relatively painless, right? Maybe now you won't dread adding a little pretty to your walls.
My little man felt the need to hammer something while Mommy was too. :)
Have you added anything fun to your walls at home lately?