Motivation takes a very subjective form in each individual (sorry for the rhetorical statement to start). I've done a few bodies of work that have taken 3-12 months to complete and for me, my motivation increases to a point and then I find I'm shooting "the same stuff" (either from the same angle, composition, critical standpoint, message to convey, techniques, etc.), which is tricky to get past. When I reach that point, I read some philosophy of photography, go through some old magazines and books by some of the greats to generate new ideas and perspectives in my approach without trying to copy them. This is usually after hundreds of shots. But this is the toughest part for me I find unless my subjects are different and the environment changes constantly. But 2 bodies of my work were done on one farm and in one shelter, so the setting never changed and the subjects were rather consistent as well, so exploring new ways to shoot the same thing was a challenge for me.
I develop the film and make contact prints as I go along so I can see what is working for me and what is not. It also deals with that human need for "immediate satisfaction". I couldn't imagine shooting 30 rolls on something and then waiting to develop it all in one shot.
I have no problem with the selection and printing part. For me, my excitement when I go through each contact sheet builds up my eagerness to print. Because I'm shooting film and am a little more selective in what I shoot than if I had a DSLR and shoot 10 FPS, it's easier for me to choose the 'selects'. I usually sit down with a bunch of beer and cigs and just go through each sheet again and again until I narrow it down to a reasonable number of selects based on my projected outcomes. This can take an entire day in itself and often requires revisiting from time to time. I'll scan the selects and edit them on the computer as my digital workprint so I can visualize and play around with burning and dodging certain areas. Then I spend at least 8 hours a week in the darkroom on the same day(s), same time(s) and stay there and print until my time is up at the very least. I think being consistant with that is important to maintain a routine between my photography and fulltime job. I keep notes of everything as well, so that when I revisit the print, I know what I did. With each print that comes out well, my satisfaction drives me.