Better method is to attach gas to the keg at ~12PSI and leave it in the fridge under that pressure for a week or so.
The shaking under 30 lbs is good if you are in a big hurry. But you can easily overcarbonate. You can have better luck if you shake it under 12 PSI because it won't overcarbonate but it still accelerates the process.
I leave mine on 12 PSI for serving, but my tap lines are long and rise 4 feet or so.
Don't over-worry. You really can't screw it up too much. It'll be too foamy or not foamy enough, both of which you can adjust.