I added a dedicated ground cable a few months ago on my Jeep. I had a length of #8 cable and a bunch of #10, so all I had to buy was a few copper lugs. Here's an edited excerpt from my build thread:
The ground wire that was connected to the sending unit on my fuel tank was pretty corroded and barely connected to the bumper. I'm thinking this is why the sending unit was burned up when I bought the Jeep...
Since the gas tank is out of the Jeep now it seemed like a good time to install the dedicated ground wire from the front end to the rear. I'll want a good ground before I put the gas tank back in with the new sending unit anyway. I ran a #8 copper wire from the rear crossmember to the front passenger side motor mount, bolting each end down with a copper lug and plenty of never seize.
From the rear lug I also ran two #10 wires, one as a daisy chain for the tail lights (tied in to the body ground at each light) and one for the fuel tank sending unit. Since I have a 20 gallon poly tank this is the only possible ground connection the tank will have. At the front of the Jeep I passed the cable through the ground lug and up to the battery. There I crimped a large ring terminal that I could screw down on the battery post. Never seize went on all the connections. All ring terminals were crimped, soldered, and heat shrunk.
I also had the bright idea (we'll find out the next time I have to pull the tank how bright it was) to put some clips on the inside of the rear bumper to keep the wiring in place.
If you look at the wiring on the right side of the photo you can see where I bolted the copper lug to the crossmember.
I also elected to replace the body ground strap to the battery. The old one was the flat braided style. It was very green and tattered. Since I have a marine starting battery I've got the screw terminals as well as the traditional posts. All of the grounds that I've added got screwed down on this screw top instead of the large terminal post. The body ground strap that I replaced was done after the other ground wires so it is a second ring terminal under the nut.
All of the exposed electrical connections got never seize on them to keep them covered.
Lastly, I made another ground cable up from the #10 wire to go from the body ground bolt through the firewall to the dash. The dash side is connected to one of the four mounting studs on the speedometer assembly. Sometimes when I work on the dash instruments I unbolt it from the body to get more access to stuff, and I'm likely to forget at first that the gauges need to be grounded if I turn power on. This way it will still be grounded and I won't accidentally burn anything up.
I don't have photos of everything, but I hope the above helps in some way (I did things a bit differently than Aaron or Shawn though, so I also hope I didn't add confusion instead of clarity).