Ill add a few to the list:
1)little or no ground coffee in the doser - a good barista should be grinding per shot. Yes they will whinge that they dont have time when they are busy, but quality is more important than convenience; maybe its time they got a second barista if they havent got time to make a decent shot
2)clean milk steaming wand - If they cant be bothered cleaning this after each use, or at least before the milk dries on the wand then you can be sure those little hard bit of crud in your latte are indeed roasted milk bits.
3)clean benchtops and coffee machine.
4) The coffee IMO is quite often not as important as some of the other rules. A good barista can make ordinary coffee shine, where a bad barista (barista isnt the right word for them - coffee seller is better) can make the best coffee taste like crud. I have had quite good coffee from Lavazza & Vittoria branded cafes on occasion. Ive never had a good coffee from a Mokador branded cafe Hmmm.
Thats enough, since im sure most of you know these tips, and there must be some more advanced knowledge lurking out there..