First and foremost in preparing your car for a battery change is ensuring that the battery isn't receiving any power from your engine. You may have found that your battery needs replacing after it failed to turn over, so your keys may still be in the ignition. If so, remove them. Without the keys, your car's electrical system shouldn't be active, which will reduce the chance of a spark or shock while you're changing your battery.
If you've already brushed on the baking soda and water solution to the terminals, you're ahead of the game. If not, go ahead and clean the terminals as fully as possible. Removing the sulfate deposits should make it easier to unscrew the nuts from the bolts on the cable ends and from the posts. Gently knock the posts and cables with your hammer to break up the deposit. Then brush on the baking soda solution and finally wipe it away with a rag.
Once the battery is cleaned, inspect it for cracks where acid might escape when you remove it. Make a mental note of these places so you can avoid placing your hands near them during removal. You might also want to place duct tape over any cracked areas to provide a layer of protection -- albeit a minimal one.
Lay your tools out on the ground. If you have a cooler top, you can lay it on top of your car's engine, but only if your car is completely cool. Otherwise, the Styrofoam may melt. Using Styrofoam as a tool tray will help prevent any accidental electrical charges that can be generated if your metal tools touch your car's metal surfaces while you work on the battery.
Your battery is cleaned, you've searched for cracks and your tools are laid out. It's time to remove your old battery.