Originally Posted by
Inertianinja
super simple
click the shifter until it's fully released (e.g. it would be on the smallest cog)
on the Rear Der, turn the barrel adjuster till it's all the way in, then out two clicks.
route the cable through. pull it tight and screw it down in the rear der (5nm)
turn the barrel adjuster out a few clicks.
turn the pedals, and shift.
turn the barrel adjuster out (increasing tension) until the chain is quiet and shifts smoothly through the gears.
Bad advice. It really isn't that simple. Every month or so there is a post here from someone who didn't know how to set the limit screws properly and ended up throwing their chain into the rear wheel spokes and tearing off their RD (or worse - it caused an accident / crash).
The Park Tool tutorials are great. If you can't set-up both the FD and RD from scratch, get some help.
I buy the inexpensive cables from my LBS ($2 each) and change them every 6 months or so (every 3000 miles or so). I used to buy more expensive cables but found that I have better luck buying the cheap ones that my LBS carries and just changing them more often. This is always a good time to make sure the derailleurs are adjusted properly.