Are you trying to carb it up in a few days or a couple weeks.
Setting at serving pressure will take AT LEAST a week, if not two.
I chill the keg, 30 psi while rolling and shaking on my lap for two minutes. Disconnect the gas and let it sit for 24 hours. Purge the gas and set to serving pressure then pour a few hours later.
Works everytime for me and I've never overcarbed with this method. I am impatient and couldn't stand waiting two weeks for my beer to carb!