1. A camera
Take pictures of every step you take when you disassemble a typewriter. No matter how experienced you are, you'll always run into one part that causes a problem. What was the front? What was the top? Does it go here? There? Does it?
2. A Dremel or similar miniature power tool
You'll spend many hours cleaning, polishing and removing rust in hard to reach places. A miniature drill, preferably with a flexible drilling tube will save you lots of time and frustration.
Dremel sells complete polishing sets for metal, including rubbing compound and steel and nylon brushes in different shapes. These do NOT include brass brushes, which you'll need for all nickel and chrome plated as well as brass parts. You may have to order brass brushes separately. Not many shops sell them.
NOTE: Always use safety glasses when working with the Dremel.
3. Screwdrivers in all shapes and sizes
Obtain a set of high quality screw drivers. Then proceed by sharpening the bits so that you may get a good purchase in the screw slots. Typewriter screws are often custom made with very narrow slots. Standard screw drivers may cause ugly burrs.
It is a good idea to magnetize the drivers or have someone do it for you by using an electromagnet. This will save you much time looking for dropped screws. It is also a great asset when putting them back in place.
A set of small pliers will help keeping a grip on small parts 'n nuts 'n bolts. Have them handy.
5. Special tools
In some occassions special tools come in handy such as nickel plating kits. They will be dealt with in the techniques section.