Make sure your pieces are dry before loading them into the kiln. Pieces that are still wet will feel cool when placed on your cheek. Wet ware can blow up in the kiln, as the water inside the clay expands.
Leave at least 1/2" between all pieces when loading your kiln. Remember that the piece will expand during the firing cycle before it contracts and shrinks.
The bottom layer of shelving should be on 1/2" - 1" posts. Your ware is placed on this first shelf, posts are set around the perimeter, and another layer of shelving placed. Make sure you leave at least 1/2" between the top of your tallest piece and the next shelf, to allow for expansion during firing. Usually for whole shelves you will use 3 or 4 posts. For half shelves, you will use 3 posts per side. Posts should be placed over each other as you rise up through the kiln.
If you have a vent, you don't have to worry about colors bleeding from one piece onto another. If you don't fire with a vent this can be a problem, so you might want to segregate colors while loading
If you have half shelves, it is perfectly acceptable to have them staggered if it fits the size of your pieces. You can even use pieces of broken shelves to add additional mini-shelves.