Automatic 20 unless you completely fuck up. When I go to sushi I usually leave 10% for the waitress and I put the other 10% in the tip jar for the fellas rolling it. Not sure if they split tips or not but I feel like they are doing more work for me than the waitress.
15-20% for a decent place; maybe more depending on certain events. Would have to be atrocious and obviously waitstaff's fault for less. Probably so bad that one would have to complain. For something like a diner, could be 50% or more--never leave less than $5 under any circumstance. Two people at a diner with a $22 bill calls for $8.
I tip 20% or more if they keep my glass full. If they let me run dry then it is lower depending on how long they make me wait. If I have to go to the bar myself or to the soda fountain then it is zero.
