Placement and Design:
Plan it out before hand. I prefer to have a blank wall space with little in front of it, except for maybe a low piece of furniture, like an accent table or a sofa table. Blending TVs into a gallery wall has also become an incredibly popular trend, but I personally tend to avoid that. It always ends up looking incredibly busy, and I imagine that watching TV would become a distracting experience with all of the artwork around it.
The shape of the gallery wall is sure to depend on what artwork/frames/items you have to create it.
Items to consider for a gallery wall:
Your own photography. What better way to showcase your beautiful work? You don't need to be a professional photographer to have some amazing shots - thanks camera phones and Instagram!
Unique, stand out pieces. Avoid stuff that's everywhere and easy to get. Gallery walls are all about you and your tastes. It should reflect them. This does not mean that what you choose has to be expensive. I would just say that it should be one of a kind. There are so many amazing, unique options on etsy and society6. Plus, you'll be supporting the actual designer, photographer, or artist who did the work.
Your own artwork. Again, you don't have to be an artist to make cool works of art worthy of display. Plus, you'll know without a doubt that it truly IS one of a kind.
Mixing Shapes. Some of the coolest gallery walls I have planned out and those that I have seen feature a variety of shapes. This includes circle frames and oval frames. Mixing those sapes with the standard square or rectangular frames is a great option - just be sure that the images, prints, or items selected for an oddly shaped frame actually fit it. More often than not, pictures can look awkward in circle frames. Another way to incorporate more shapes: mirrors and wall clocks.
Mixing Colors. Do not feel like you have to have the same colored frames. Different colors will add a lot of visual interest. If you do choose a more vibrant color, especially if it's a metallic like gold, be sure to tie in to other decor in your room. Having random colors on the wall when they are nowhere else to be seen makes for a not-so-cohesive space.
Silhouettes. I totally made one of these for my dog - I got the idea from a friend and apparently there is an etsy shop that does just that. But you can do it yourself as well. Here is an amazing tutorial that I used. Silhouettes are just so classic, work well in smaller frame, and I would definitely say they are a trending item to have in your home. The best thing about them is that each silhouette is still going to be different.
Parting words: the more unique and the more you that something is, the better choice it will be for your own gallery wall. If you like it, put a frame on it.