Well just wrote a lengthy response, then hit a wrong key and deleted the entire post. Soooo, trying again. I am a fairly new collector, 2 years, so far far far from an expert. But my 2 cents:
Playfield: Clean fairly gently with Novus 2 ( you can get from a number of pin suppliers ), then 1 or 2 coats with good carnuba wax. depending on play, rewax every 6 months or so.
Bulbs: You will get strong opinions both ways. I converted 1 of my 6 em's to LED. Used clear lens below playfield and white above, all warm white. Like that it brightened the game, but you do lose some of that em warmth of incandescents.
Sounds: Will let more expert Pinsiders guide you on this. But in general light buzzing I just check to make sure isn't something arcing or otherwise obviously wrong. Loud sounds / buzzing get immediate attention.
General maintenance: Make sure all contacts and switches are adjusted and cleaned. Surprising how much this can affect game play. Make sure game UNPLUGGED before working under the play field. Always use new pinballs, old dull pinballs make those lovely swirls you see in the paint of many em's. Clean play field glass often. Check condition of paint on the back side of the back box glass. If any flaking, search Pinside for what to do about flaking paint. Keep playfield, flipper, and shooter tip rubbers fresh. Replace when cracked or worn. Make sure the machine is level side to side, and set to the angle you like front to back. The angle can make a real difference in fun factor of playing.
Gotcha's: Lots: Number 1: When working on the machine make sure it is unplugged, not just turned off. Surprising where there is power even when you don't think there is. 2. Be careful how aggressively you clean painted surfaces. 3. Never set or let guests set drinks on top of the machine. 4: Pin addiction. Bought my first game, 4 days later second, within 5 months was up to 6. Now at 8, and out of room in my garage playroom. Thankfully my wife keeps me from getting too addicted by banning games from inside the house.
Good luck and enjoy.