Old microwaves are between the easier to move and disassemble old appliaces. All you need to scrap a microwave is one or two screwdrivers.
As always happens in old appliances, depending on their status you should decide if it is better to dismount and sell the old parts, repair or scrap them.
As for scrap parts, what you should look for is: wires, motor, transformer and magnetron. They are all worth for the copper the contain.
Magnetron, motor and transformer can be sold at motor price at the scrap yard or can be dismounted to remove the copper coils. The latest can be sold at copper wire price.
If you decide to dismount the magnetron pay attention to do not break the ceramic antennas. They contain dangerous chemicals.
Microwaves also contain small capacitors. They can be dismounted and sold at the yard at mixed metal price.