http://www.pirate4x4.com/forum/showthread.php?t=869210 is a good example of what not to do. See my response on page 2 for basics of how to get a feel for welding. Also, local community colleges usually have a welding class that will usually net you a certificate of some sort, and they are typically inexpensive and reasonable hours. Good affordable Mig welders for intermediate use such as working on vehicles are the Hobart Handler 210 and Iron Man 230, they can weld all steels, but if you ever plan to weld aluminum, they have an add on kit called a spool gun welder that allows for Aluminum welding as well. Another is the Hobart Handler 187 if you don't need to weld aluminum (most of us never do). Also, don't get confused when you see Weld Thickness: x" on these welders, as thats single pass penetration ability. For example, if it will do 1/4" single pass, you'd just end up doing 4 or more passes to bond 2 pieces of 1" plate. There are two different types of welding wire also, flux core and solid wire. Flux core doesn't need shielding gas, but produces a lesser quality weld, whereas solid wire uses a shielding gas to allow for optimum weld effectiveness.
Things to look for on a 4x4...
Mud where it shouldnt be, like on the inside back wall of the driver side of the cab, on the under side of the hood, in between the leaf springs, on the firewall, in between the cab and bed, inside the box part of the front of the frame, down in the crevices of the core support, etc.
broken springs, anything welded onto the frame, wiring that has turned green or been spliced, rust holes, worn or broken steering parts, you name it.
basically, imagine the truck when it was new, not as a complete vehicle, but as a group of systems and their components,then picture what you want it to be, and determine how many of the issues the new vehicle has that will cause you problems in your build. I don't even see a car as a car or a truck as a truck anymore, all I see are the systems and components that make up that vehicle, and I choose (or compile) the combination that suits me the best.
This is one skill that is important to become a good mechanic/ fabricator. Another is being able to look at something and figure out what tools you need to do a job, and what tool will work the best. Also, being able to look at, say, a front axle and know what it will take to get that out from under the truck, and a new one in its place, right down to torches for heating up the nuts and the steps you need to take to get that axle out.