A group of pictures on a wall is one of the cheapest changes available to a room and one of the most frequently botched, because it is usually attempted directly on the wall with a hammer in hand. Done in the right order it involves one round of holes and no arguments.
Start by choosing the group rather than the wall. Gather everything that might go in: prints, photographs, something framed that has been in a drawer, a page from a book that deserves a frame. A group made entirely of matching frames reads as a set and is easy but bland; a group with two or three frame types and a consistent gap reads as something that accumulated, which is usually the better outcome. If the frames vary a great deal, pull them together by repeating one thing across the group, most simply white mounts of the same width.
Lay the whole arrangement out on the floor in front of the wall it is destined for, and give this part most of the time. Two rules carry the composition. First, the outer edge of the group should form a recognisable shape, usually a rectangle, even though the frames inside it are different sizes, and the pieces on the outside should be the ones that hold that edge. Second, the gaps between frames should be consistent, somewhere between five and seven centimetres for a domestic group. Uneven gaps are the single thing that makes a gallery wall look accidental.
Put the heaviest visual weight low and slightly toward the centre. Large or dark frames at the top of a group make it look as though it is about to fall over, which is an odd thing for a still arrangement to communicate and yet is unmistakable when it happens. Move things around until nothing pulls the eye out of the group at a corner.
Now transfer the layout rather than measuring it. Cut a sheet of paper to the size of each frame, write on each sheet which frame it is, and tape the sheets to the wall in the arrangement you settled on. Newspaper, wrapping paper or lining paper all work. This is the step that removes all the risk: you can stand back, move a sheet three centimetres, and repeat that as often as you like without putting anything into the plaster.
Set the height while the paper is up. As a rule the centre of the whole group should sit around a hundred and forty-five to a hundred and fifty centimetres from the floor, which is roughly eye level standing and is where pictures are hung in galleries. Two situations override it. Above a sofa or a chest, the bottom of the group should sit about fifteen to twenty-five centimetres above the furniture so that the two read as one block. In a room used mainly sitting down, drop the whole group a little.
Then mark the hanging points through the paper. On each sheet, measure where the hook will need to be for that frame, allowing for how far the wire or hanger sits below the top edge when the weight is on it, and mark that point on the paper with the pencil. Put the fixings in through the mark, tear the paper away, and hang. Check the first one with a spirit level and then check the group by eye, because a frame that is technically level next to a wall or ceiling that is not will look wrong and should be adjusted to the room.
If the wall is plasterboard, use a fixing rated for the weight rather than a nail. Small frames will hang on a picture hook almost anywhere, but anything with glass and a wooden frame is heavier than it looks, and the failure happens at three in the morning.