I've probably put a couple thousand feet in over the years, (which really isn't much). It's not too hard to do though.
Cat 320 is correct about the gasket and lube. (For that type of joint anyway--some pipe joints slide together much like plastic sewer pipe, but for most of the valves and fitting you'll find the "mechanical joint" type.) Make sure you put the gaskets in facing the right direction. If the materials are already on site, I imagine the lube is there with it. It's pretty much the same stuff as is used with rubber gasketed sewer pipe. An old paint brush is real handy for applying it, but it can be done with your hands too.
The easiest way to put two lengths of ductile together is with a wire rope choker and a good operator. Pick the pipe up at the center point, and have the pipelayer guide the spigot end into the bell of the previous piece. Lower the pipe so that's it's resting on the trench bottom, and then curl the bucket out gentley. The joint should slip right together. Otherwise, you can usually pry the joint together with a digging bar.
There's a certain amount of deflection (for gentle turns, or grade changes), that's possible in each joint, but it's easiest to have them lined up straight to put them together, and move them afterwards.
Mechanical joints are different. You'll have an iron ring, with bolt holes around it. That's called the gland. The valve or fitting will have a correpsonding series of bolt holes. You'll also have a different type of gasket. Slip the gland over the pipe, and then slide the gasket onto the pipe. Put the pipe and fitting together. There's a raised edge on the gland, on the side that faces the fitting. You can use that edge to push the gasket into the joint, It should go all the way in, and be even all the way around. Insert the bolts throught the holes, threaded end pointing towards the pipe. Tighten the bolts evenly, and take care not to overtighten.
Some authorities require a ployethelene plastic sleeve around the pipe. It's easiest to slide that onto the spigot end of the pipe before lowering it into the trench, and then slide it forward once the choker is unhooked.
Some authorities require sand bedding, others don't. Ductile iron is pretty tough stuff. Certainly you wouldn't put any big rocks around it, and you'd try to be sure it's bedded well, but it's not going to sag or go egg shaped like plastic sewer pipe might.
Anywhere you put a fitting (a bend or tee), you'll need to back it up with a "thrust block". That's a clump of concrete you pour between the fitting and the undisturbed dirt behind it. If that's not there, the joint can push apart from the water pressure.
There's more, but that's the basics...
Good Luck!