Step 1: Background
Naturally, the first thing I discovered was the robot's diagnostic mode... this was before I knew such a mode existed. Here's information on Diagnostic Mode for the older generation. Pay close attention to over current warnings as these will cause damage in the long run.
Below you'll see the classic Roomba spiral footprint on my ugly apartment carpet.
iRobot recommends cleaning every 2-3 cycles (the original manual says 5-10 cycles I think). Die hard Roomba owners clean their brushes every use. Not to worry though, it takes a few minutes - much less time than vacuuming would. Cleaning keeps everything running more efficiently, cooler and thus allows a longer robot life.
Step 2: Begin Cleaning
Now, flip your Roomba on its backside.
Step 3: Remove the Vacuum Service Cover
Remove any dust inside and set the cover aside.
Notice the interesting eddy patterns caused by the spinning motor and dust slowly clogging from one side.
Step 4: Remove Brush Grille
Now remove the top middle section and then press in on the sides to remove the left and right section.
The grille should now be out. Clean as necessary and set aside.
Step 5: Remove Cleaning Brushes and Bearing Carrier
Now, gently pull up the the bearing carrier. The brushes should come up with it. Lift it out of the robot and pull to the right to remove the brushes from the driven side of the robot.
Step 6: Cleaning the Brushes Et. Al.
Now remove any tangled bits around the brass bearings and clean off any dirt/debris that may be inside the carrier. Do the same for the driven side of the robot (see picture).
This is also a good time to remove anything that may be caught in the spinning whip brush. This can be removed for cleaning, but I'm not going to do so often because the screw strip easily.
Step 7: Cleaning House
When done, take a peek inside through the particle bin hole. If you see any fuzz or anything, pull it out. Having a toothpick handy helps.
You may also want to peel back the wheel treads and looks for anything hiding in there.
Finally, I used a canned air duster. I sprayed into the particle bin gap under the brush housing etc. The idea is to push everything out the leading edge of the cleaning portion of the robot. Be careful, because this can cause more damage than good - especially if large clumps of dust attach themselves to the motors (which may cause overheating).
Step 8: Front Wheel and Lubrication and Reassembly
The mfr says nothing about oiling. But Volkswagen also says my gearbox is oiled for life (oil testing proves otherwise). We're going to oil some friction components with a mineral oil - like sewing machine oil.
Apply some oil the the bearings and bearing carrier. Where moving parts come near stationary parts. Apply a drop around the whip brush. Apply a drop or two into the front wheel. Apply wherever you think it is necessary. Just don't apply too much that it will damage your floors :P
When done, reassemble reverse of assembly. If you had any over current warnings before - check again. A good cleaning typically resolves that problem.