Some tips:
Angled adapters for compression fittings are useful for getting tubing around the case.
Thread extenders are invaluable. Buy a few, you won't regret it.
If you're fitting a radiator internally, at the top of the case, measure the clearance from the top of the motherboard to the case roof. For example, the CM 690-II Advanced only has a clearance of 45mm, meaning that you'd need to use a slimline radiator.
It's better to have fans pull air out of a radiator, than trying push air through. So, using that top-mounted radiator as an example, the fans should sit on top of the radiator (in the case of the CM 690-II Advanced, you can mount the fans on top of the case rough and place the top case shroud over them).
Radiators again: beware that some radiators mount the barb holes quite far apart. With the Swiftech MCR220QPK, this meant that one of the barb holes was obscured by the ports on the motherboard backplate and I had to reverse the mounting of the rad so that the barb holes were next to the 5.25" bays. This caused me some cable routing problems, but isn't the end of the world. Still, you'll probably want to make sure that the barb holes on your radiator are a bit closer together.
You'll still want some regular case fans to pull/push an air supply through the case: this is necessary for cooling the motherboard chipset and the RAM and will also help temperatures in your loop.
Check the clearance from the top-mounted radiator to the back of the case, where the 120mm case exhaust fan goes. A slimline rad will probably be okay, but larger rads will mean that that case fan will have to be mounted externally. This isn't a problem, but you will need to buy a fan grill to cover it.
Before you mount your radiators, you should flush them. Rads tend to build up impurities sitting on a shelf for so long, and if you don't flush them before you fill the loop, those impurities will come out during operation and you'll see stuff floating in your tubes! To flush a rad, get some distilled water (doesn't need to be expensive coolant, you can get distilled water cheaply off eBay), boil it, leave it to cool for a couple of minutes, pour into your rad, seal the rad with the plugs that came with it, shake the rad around for a few minutes, repeat until the waste water runs clear.
Avoid AC Ryan gear, especially their radiator grills - they aren't drilled correctly and don't fit 15mm fan spacing even though they're advertised as doing so.
