For the last 10 days we've been hanging pictures on our walls. Most are oil paintings we've bought over the years. We have quite a collection.
Every two to three days we'll hang 4-8 pictures.
I've found that the best hanging kits are the brass ones, with re-usable nails. I don't know which store it was, but one sold a kit with about 25 different types of hanging parts. Hanging parts ala carte are very expensive when you buy them separately in quantity.
In the past I used to put tape in a cross and then nail into the wall. After removing more than enough plaster from the walls of my rental, I've decided that fine brass hanging nails can be emplaced and removed without using tape - they actually pull out cleaner.
The other nifty trick I've learned is to use a two levels - a long one and a short one. It's much easier to align two hooks for a large painting or obtain the proper intersection of the x and y axises when marking a hook location. Once the picture is hung, I place the level against the bottom of the picture to make sure the picture itself is level. I'll also measure the distance from each side to make sure it's in the correct location.
One tool I wish I had was a t-square. It would make position x's for individual hooks much easier as you could measure out horizontally from the right border and then upwards from the bottom very easily. Ideally the tsquare would have levels - so I wouldn't have to draw bottom and right margin lines.
One important trick. Always measure the distance from the bottom of the painting to the highest point the hanging wire will hang on the hook(s). Also, make a point of measuring the distance between the hooks if there are more than one. It will be very helpful in determining hook location on the wall.
Also, for less than $3.00 I picked up a large package of wall protectors at Lowes. These are plastic bumps that go on the back of the painting and prevent it or it's frame from scratching the wall. As most paintings hang outwards, the most important locations are at the bottom and lower sides of the painting. The larger / big plastic bumps are the best, the small ones being of minimal value.
Mounting the pictures on the walls makes a really big difference. The house feels warmer and more homey. Then again, some pictures won't feel homey, such as a Picasso print, The Scream or a Andy Warhol piece. I think impressionist pieces are particularly warm and comforting for a home, such as Monet prints, etc..., but everything is in the wallet of the owner.
Have a wonderful day,