This gut instinct served me when I was creating my gallery wall for our living room. Here are some "rules" from a non-designer.
I knew that when the TV was turned off, we had a huge negative space black rectangle on our wall on a neutral colored paint, so, in order to soften and meld with the large, black TV, I did black and white objects all around. When we first moved in, I had bought a large colorful painting for the side of the TV, and it was SO busy. When the TV was off, it wasn't a balanced look--your eye was drawn to the large, black hole of a TV on the wall, and when the TV was on and had colors moving all around, it was a busy, competing, mess of a wall design. I make mistakes and I learn. Maybe it was just the colors and pattern I had, but it definitely didn't work.
If you have a large flatscreen on a neutral wall, I personally recommend using black and white pieces around. The white softens the negative space of the black and the united colors tie it together, almost creating art out of your TV. If you do splashes or pops of color to tie into your room, that works too--just keep it balanced around other neutral shades.
I am using color (shades of light blue and rust) in the chair pillows that will be on the chairs I will place on each side of the console below the TV (still to be found and bought), in drapes on the other side of the room, and on the couch pillows on the other side of the room. A canvas artpiece next to my fireplace wall (adjacent to this wall) has oranges and blues in it too.
I also knew that with that large of a wall, I needed weight in the size of my pictures. When you get too many small pieces, the wall gets busy and cluttered--floating all over with nothing centering and weighing the space down. So, my frames are mostly large (they don't look huge, which shows you the size of that wall!), with one or two small accents thrown into the grouping.
(We have a big slider behind me that causes glare, so I apologize that some of the pictures have that glare)
I also wanted a set of "three" (that perfect design number we hear about) look of appearing on my wall since it is long and narrow. I essentially used the TV as my center and then two clustered groupings on each side--connecting it all with the top photos above the TV. The color is uniting it all together as well.
Side grouping on one side of the TV
A closeup of the other side grouping on the other side of the TV.
Today, I also learned a rule from Sarah 101 for gallery groupings. I actually followed this rule unknowingly. Pick either the bottom or top of the gallery wall to be lined up. The opposite side can be at different heights. As you can see from my pictures, I, in essence, unknowingly lined up the top of my gallery wall in a line (with a slight alteration in line above the TV, which works with the long wall and high ceilings we have). The bottom is all at different heights, which works since the top is structured.
See how the top is in a straight line (with a purposeful rise in the line just above the TV) but the bottom is at all different heights. . . The line on the top or bottom helps anchor the gallery.
You want to keep any groupings equally weighted but not too matchy matchy. Each side of the TV is in a different grouping, but they have equal "weight" and substance to them. You can see in my pictures above that each side is in a different formation, but they each have 6 pieces and have something centering the "circular" arrangement around them. On one side the "H" is anchoring the group and, on the other side, the canvas topography is centering the grouping.
I've tied all these "pieces" together to avoid a cluttered look. In my gallery, the colors of black and white, the lined up top, and the two topography canvases tie the sides and groupings altogether.
I explained how I figured out my design here. In summary, I cut out pieces of paper the size of my frames and TV and practiced the designs on the floor until it looked right. Then I taped the papers on the wall to see it there and just attached the frames by removing one paper at a time.
Happy gallery wall planning!