I have never had to do a U-joint before
This thread has a couple useful links.
Another thread.
I swear we recently had a discussion about doing universal joints when you have 0 experience with them. I can't find that thread now.
Anyway, replacing universals isn't that hard. The most nerve-wracking part (I think) is making sure you don't knock a needle bearing out of position when installing the new caps.
You also must be sure to press in the new caps straight, so they don't bind up. I apply a bit of quality nickel anti-seize to the caps before installation to help them slide in.
The rear driveshaft joints are a bear to do because they're large and are of a tight press fit. I wrestled with them for awhile. I used Precision 351A's (which are slightly different from 351's), but had to grind the snap rings thinner so they'd fit back in their grooves.
These days I usually use a 2. 5 lb hammer to drive the new caps in. I also have a 3-ton arbor press, but I really need to make a cheater pipe for it. The hammer actually works a little better for me.
There are various "tricks" to removing and installing them, with no 2 people doing it exactly the same way. The best way to learn is to have someone with experience show you how to do it.
When you grease them, pump until grease oozes from all 4 caps.
Ryan