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.
Oh don't give me none more of that Old Janx Spirit
No, don't you give me none more of that Old Janx Spirit
For my head will fly, my tongue will lie, my eyes will fry and I may die
Won't you pour me one more of that sinful Old Janx Spirit