Preparing to build a computer is fairly simple, first step is to make sure you have a nice clean open space. Give yourself room to sit, while the parts and tools remain safe and clean.
Before you open up any of the boxes containing your parts make sure your grounded, touch some kind of object that is touching the ground, preferably a metal chair leg or something.
This will discharge any static that you may have built up in your body. Static is very bad for computers.
Attach the grounding strap to your wrist and to some object that will keep you grounded.
Avoid having any food or beverages near the area you will be working on.
That is pretty much it for prep.