How to hang artwork
To begin with, if you can have two people help the process--one to hold up the artwork and the other to direct--it will make it easier. It can be hard to figure out the location without standing a distance back from the wall. It is, however, possible to do it yourself with some practice.
There are always variables, but a good rule of thumb is the centre of the pictures should be around 60" to 66" above the floor. If it is a tall, rectangular piece, imagine it divided into three (from the top to the bottom) and place the start of the top section at 60" to 66" or so. Usually, pictures shouldn't extend past the edge of whatever is below them. It will end up looking top-heavy. Have some space beside the pictures from the edge of whatever piece of furniture is below the artwork.
Now, if you have a group of pictures, imagine them as one big picture. Lay them out on the floor first, measure how wide and tall the grouping is, and then mark out the extents of the grouping on the wall. From this you can locate where to put each hook or nail.
Still, the key is to make sure it is in proportion to what is around it. You really don't want whatever you are hanging to be too close to the ceiling or too low. For instance, in a bedroom where you don't have a headboard lower the pictures above the bed so there isn't such a large expanse of wall between the two. If you do have a headboard make sure that there is some breathing room between the pictures and the headboard. The squished look isn't ideal, neither is having your art look like it is floating and not relating to what is around it.
Look at these two pictures. The one on the left has the art placed a bit too high off the bed, plus it is out of proportion to the furniture below in width. It needs to be wider. The one on the right has the art hung a bit lower and it now relates well with the furniture. The overall width of the art could be smaller, but it does work. Having 3 of these pieces of art would also work here.

In living rooms, though, and anywhere where you spend more time sitting than standing, having the pictures a bit lower can make the room feel cozier. Having them higher on the walls disconnects you from them and can make the art feel like it is towering over you. Always remember how the room is being used and what the art is relating to.
We should address hanging flat screen TV's, too. These are often hung incorrectly, and half the time it is because people want it mounted above the fireplace mantle, and the mantle is usually the ideal height that the TV should be at! The TV really should be hung where it can be at the right height to comfortably view it and if the fireplace is in the way, so to speak, the furniture arrangement should be adjusted so that the TV will be viewable from a different spot.
Instead of getting too technical, the simplest and most accurate way to know the height your TV should be at is to measure what your eyelevel is when you are seated to watch TV. If you are a bit off that is ok. Whatever that measurement is, or the average eyelevel height of the people in the house, should be at the middle of the screen. If you have to tip your head back it is too high.
If you get stuck, remember, we can help you with the hanging.

