Firstly, make sure you have the following tools/material on hand: very tiny screwdriver, normal screwdriver, flat-head screwdriver, bag or container for the screws, bag or container for the parts you want/don't want, and newspaper for glass
There are a lot of screws! First step is to locate and remove all screws.
Second step is to remove any plastic parts that can easily pop off. Be careful not to rip apart anything although some parts may require a lot of force to pop out.
Third, remove the scanner portion. There may still be hidden screws - remove them. There will be a headers and ribbons, be careful not to tear these. You will be able to remove the header from its port (especially easy for those with tiny fingers).
Once you are able to separate the top and bottom layer, you can begin further disassembling either layer. For this, we will first finish off the top layer because it has less parts attached. The top can possibly have one motor, and a pulley at best. The more useful parts are in the bottom.
For the bottom, make sure you remove any cartridges. Then you can remove the cartridge trays. Since they sit on a metal pole, you must work around the pole before removing the pole itself.
At this point, you can now extract various motors, pulleys, platforms and other useful parts.