First off, don’t be purposefully going to restaurants or other places where you KNOW there’s tipped staff (this is probably 95% of sit-down style eateries in the US). I understand that you can be dragged into situations, but try to avoid this.

Once you’ve accepted this first rule. Let the server know they’re great FACE to FACE. Sure, grabbing the attention of their manager may do them some favors, but that isn’t always guaranteed, and this could be time-consuming for you and your server. Maybe this is just me, but if a server really made an impression on me I’d like to do the same by genuinely thanking them and letting them know they’re great.

If my service isn’t anything special or bad even, I still tip a minimum of 20% without saying anything.