Setup the game on legs, and take off the glass. Physically touch and inspect every part on the playfield. Look for loose or missing nuts, screws, posts, inspect it all.

The reason is, anything you catch now won't be a problem later. A loose post that is tightened correctly can't damage the playfield by getting hit with the ball. Then a coat of wax on the playfield (a good paste wax with NO cleaners). Most of the time I throw away the balls Stern sends and put in top quality ones. Finally, close it up and play the first game. Pay attention to switches registering, smoothness of the ramps, anything that feels wrong. A couple of switches will probably need adjustment now. Are the slings how you like them? Does the scoop eject well? Just the "play" features you need to dial in to get them right.

Then play the crap out of it. ST is a great game.