If you're a waiter or waitress, please be sure to check if I need another drink.
I'm sure this is waitstaff 101, but I'm surprised by how many still seem to not pull it off. I tend to be a generally parched individual, and someone who likes his beer, wine, cocktails, and bottomless ice water, so perhaps I'm hypersensitive to this.
But my dining-out-math tells me this is probably the single most important factor in how much my waitperson gets tipped. I'm not going to blame them if the food sucks (generally), why should they be punished for a bad chef? My tip is almost exclusively based on how attentive they are, and on the size of the bill. Both of those are augmented by offering me extra drinks.
Man, I'm thirsty.