It is well-known that practice makes perfect so the best advice you can hear from everyone how to type fast is to practice, practice and practice. If you're typing texts at least 1 hour per day, within time your skills will be on a higher level. Don't forget about your posture 'cause if you're feeling a backache or pain in the neck while typing it is the worst. Next time you'll associate typing some documents only with pain and unpleasantness.
Another tip - don't rush, use all your fingers, play games (there is a plenty of them online or as mobile apps) and have a break when you're tired and feeling you're wasting your time. Be patient and study smart!
However, if you're too busy to do, I would say, such secretarial work there are online companies like this professional typing service, which are by cost-effective prices will relieve you from such routine tasks so you can concentrate on other more important tasks.
Anyway, good luck!