The first thing is deciding the components you want cooled. Components you can watercool are as follows: CPU, GPU, Northbridge, RAM and the Voltage Regulation Modules, or VRMs. For the case of this tutorial, I will only be cooling the CPU, as that is what most first time users should start with.
The next step is to find a CPU block that fits you're CPU socket. I use an FX8350 on an AM3+ board, so I would be looking for water blocks that fit the AM3+ socket. Then it is about the aesthetic component, and the reviews. In terms of block quality, the shinier the surface the better, and it should certainly be copper. I went with the Apogee HD water block, for which I had to request AMD mounting hardware. While I was at it, I picked up some better thermal paste, but the block comes with some.
The next step is to find a radiator. For those of you who have 240MM or 360MM fan blowholes on you're cases, one radiator will suffice for CPU cooling. If you have only 120MM fan holes, you will need 2 radiators if your CPU has a ~120W TDP or more. Copper core radiators are the best, but are also the most expensive. Radiators come in black and white usually. I decided I wanted a 360MM radiator and mounted it outside my case by drilling holes through the top.
Now you need a reservoir and pump. The reason I grouped these two together is that there are many ways to combine the two. There are pump reservoir combos, where the pump is built in or mounted to the reservoir, separate pumps and reservoirs and radiators with integrated pump and reservoir. Generally speaking, when it comes to reservoirs with pumps mounted on them, the D5 or dual D5s are the best. They produce the least vibration against your hard drive rack, lowering overall noise levels substantially. With separate pumps and reservoirs, any pump will work, but the D5s and DDC pumps like the MCP35X are some of the better ones. I went with an on-radiator res and pump for this tutorial.
The next step is easy. What type of tubing do you want? There are two main types, flexible and rigid acrylic. Rigid acrylic does not bend, so it is imperative that it is cut to the proper length. It also requires compression fittings, rather than barbs. In my opinion, flexible tubing is much easier to work with in smaller cases, so I went with it. I bought 7 feet of PrimoChill Advanced LRT in white, and some anodized black G1/4 barbs. I also threw in come hose clamps, (black anodized) to help prevent leaks.
The next few things you need are pretty simple. The first is fans. Ideally you want 120MM (depending on the size of the radiator) PWM fans with high CFM and low DB emissions, about 22db. The radiator I bought (MCR-X20 Drive Rev3) came with fans, so I did not buy any. I used my integrated case fan controller, but I would advise buying one if you do not already have one lying around. Then, I had to decide on coolant. I purchased 32oz of PrimoChill PC Ice in clear, which is anti-microbial and non-toxic. If you choose to buy tubing that is a color, like I did, don't buy colored coolant, as it will stain the tube.
Then, once your order arrives, follow the assembly instructions given. As a comparison, my FX8350 with the components I purchased in this tutorial idles at 9C socket.