Step 1: Hole / Fan installation in case
What you need is a hole in the side of your case, that is going to suck in cool air and blow it onto your preferred components. I chose to make my fan blow directly onto my CPU since I bought a big ol' heat sink with fan already. Specifically I purchased the Thermalright XP-90 shown here and below.
Some tips for this step are:
1. Be EXTRA careful to try and line up the hole you are cutting EXACTLY over your CPU, I used a laser level dohicky for this.
2. Also know your materials and what it takes to cut it, not all cases are made the same, some of the new aluminum models would probably be cut fine with a dremel but I had a tough steel case which I went overboard with and cut with a plasma cutter basically just because I had access to one.
3. Depending on your fan size and case you might have to improvise with the hardware, I thought I could get some screws to mount the fan on the case at a local PC shop but I ended up just going to a hardware store and getting some long screws, rubber washers (reduce vibration noise!), and nuts.