I've done four lagers since getting a fermentation chamber - a Schwarzbier, Traditional Bock, Bohemian Pilsner, and Oktoberfest... so, I'm hardly an expert. But I'll tell you my approach, which is based on a lot of what I've read.
You CAN do the approach where you pitch the yeast warm, wait for fermentation to be visible, and then drop the temp to 50 F. This way, however, produces more diacetyl. So, I follow the Narziss method (I think that's how it's spelled). I pitch at about 45-48 F, set the temp of the fermentation chamber to 50 F, and let it go. Fermentation is obviously slower to start, and not as vigorous as at ale temps, but it'll get you there IF you pitch enough yeast (important).
Once it starts to slow (ideally when the gravity reads about 4-5 points away from your target FG... not a bad idea to check if you want to be sure), I'll take the carboy out of the chamber and leave it at room temp till it rises to about 65 F or so; leave it there for a couple of days for the diacetyl rest. Then, I put it back in the chamber, and decrease the temp by about 4 F every day until it's back down to 50 F. I'll leave it there till it's been in primary for about 3 weeks.
After that, you DO have to rack to secondary; this is where the lagering takes place. Since you keg, I'd just rack to the keg if I were you, and do the lagering in there. I then lower the temp of the chamber by about 1-2 F every day. If you dropped it from 50 F to 34 F (or whatever you want to lager at) right away, the yeast would just floc out; do it slowly so they have time to adjust. I've read some opinions that the yeast won't be active anyway below 40 F, so whether you choose to lager at 32-34 F or 40 F is up to you. Once you get to your lagering temp, leave it there for however long you choose to lager. I'd go at least a month; it really depends on the beer. If it was a strong Doppelbock, for instance, I'd probably lager at least 4 months.
When I bottle (obviously won't be an issue if you're kegging), I add about 1/4 pack of rehydrated dry yeast to the beer in the bottling bucket, to make sure it carbonates after all that time at near-freezing lagering temps.
Have I forgotten anything?