The first rule to making a gallery wall is that there are no rules. The most important thing is that you carefully choose pieces that captivate you, that enrich your life or that make you feel one way or another. Art is a powerful and demands attention and is perhaps why I love it so much.
Now, there are a few things that will make your gallery wall come together.. one is that you should have a variety of scale (size) and both pictures that are landscape and portrait. Remember, how you approach this will be reflective of your own personal style. For example, some people have to have all white frames with the same thickness and the same matboard surrounding each picture. I on the other hand like to keep things interesting - for me, consistency can be achieved by ensuring that each frame has a gold detail (in various finishes, thicknesses, styles). There is no right or wrong way to go about what pleases your eye but you should approach this project with a willingness to play.
Nina and I will start with a bare canvas, our many white walls, and then just start with "Try this one there.." or "Ok, now what about if we moved that beside the other one?" Slowly, it starts to come together like a puzzle, the pictures start to compliment each other and begin to look like they belonged their all along!