Manipulation can be quite important in the game.
After character creation, the best way is with books.
If you start the game as a slaver your manipulation should be around 65. (without any points in stats)
This value will easily increased by the usual actions your characters takes as a slaver.
Yes this is a very grindy game. Look for rem'py tools that will edit your saves.
The game also has the enhanced version which allows a more sandbox play style.