Well, as for many joints, timing is key. It can be both really (extend/contract)...
You see, what I do is get to the point where I know I can grab whatever body part and edit it from there. I contract at certain points and extend at certain points. Sometimes I even go back and forth between the two...
It's really hard to explain, rather something that you just learn over a long period of time.
Also, relaxing adds more freedom to the wrist, so that may be one of the best ones to start out with and work your way up to contracting it at the last second.