I don't want to make another detailed writeup but more of a generalized guide and leave it open for discussion.
Grease is one of those items that may get overlooked on our maintainence lists if we aren't changing the oil or replacing drivelines. There are some other important reasons to grease other than just basic lubrication. The first is the reason I felt compelled to bring this up: water. Tis the season we go splashing around in mud holes and traversing flooded streets with über-confidence in our jeeps and it could be the thing that's the most detrimental.
We always have a flash of an image of a snorkel when we think of water crossing and some of us who have the experience know that our distributor cap is also at risk. Vents are up high for the transmission, transfer case and both axles but what about the rest of the vital components? Remember that pressure washing the mud off the jeep will put water in places it normally wouldn't get there on its own. Expelling water from rust friendly parts should be very high on the list of monthly (if not biweekly for DD) chores for keeping the jeep healthy.
The last reason to grease is to give us a good chance to have some intimate time under the jeep poking and prodding around. Inspection on a very frequent basis should be paramount to anyone who wants to have a functional vehicle. Any damage you can avoid is a big point in the W column. All the grease zerks on the jeep are connecting the most vital (and expensive) parts that make the jeep go.
On the basic Yj, there are a few zerks to attend to. There are the ball joints thigh connect the knuckles to the front axle and all the steering components (4) two on the drag link and two on the tie rod connecting these aforementioned knuckles. All of these are easily accessible with the tires and wheels on and the jeep on the ground. You may have to turn the wheels one direction and then the other to access them but easy nonetheless. Then comes the driveshafts. The front driveshaft should have two ujoints which are both usually greasable on the crux of the joint kind of hiding in the corner. If your cad is still working then you can turn the shaft by hand and access the front easily and the rear if you have stretchy arms. There is a third on the slip joint that may squirt a bit out and tell you if your seal is no bueno. The rear shaft is pretty much the same without the slip joint being greasable as it is lubed by the transfer case.
If your transfer case has a SYE then you have a cv joint installed on your new shaft. There are four greasable points on this type of shaft. Three ujoints (two are usually greased ok the caps and one on the crux) and the ball type cv joint that maintains pressure on the two joints so the angle can be evenly split and you avoid vibrations. Many of you may have better luck than I do but the cv joint is not accessible in the installed position and must be taken loose from the transfer case to be greased. Do not shortchange this joint!!! Mine went out within 6,000 miles despite being greased several times.
When it comes to types of grease the possibilities are numerous but most lithium based automotive grease is perfectly fine for all your needs. I have used the red and white auto grease and the high pressure blue, green, yellow (cheapest) and the silver which is my favorite. Some grease is better than no grease.
As for hardware, I suggest a Lincoln grip type gun over any battery powered or pneumatic guns on the market. I grease a lot as a farmer and my forearms look like Popeye because of it (yeah right that's all) so stick to human powered guns. The others can be dangerous when accompanied with accessories. The standard gun will come as either a stick or hose adapter and I suggest the latter. The stick is great for a two handed gun but is hard to get into tight places unless you use the mini guns.
Most zerks are a standard size and are a ball type that all guns will adapt to out of the box. There is also a needle type zerk that is almost always found in the cv joint and sometimes on the endcaps of ujoints. You'll need an adapter. A good adapter. Once again I suggest Lincoln but don't skimp on an autozone special here. I broke three of them before I got the right one. Looks like this.
If you guys have questions or want to discuss further please do so. I will answer what I can and if I forgot something or have incorrect info please tell me. I'm sure there are other greasing threads but I'm just giving a little info inserted into a section that needs to know.