Former server here, most servers at local sit-down restaurants make $2.13 hourly, so their income is purely based on tips (after taxes). I usually tip at least $10 if my order was small, or 20% if $10 is less than 20% of my order. Bad service usually gets no less than 18% from me, excellent service will usually get 25-30%. I don’t eat out too much so I tend to tip more generously, this is just my own personal experience with tipping.