I've learned a lot about restaurants since working as a waitress. Granted, I haven't been at it that long, but there are consistently some behaviors that IRRITATE me. And there are others that I simply didn't know about. I think it should be required that each person spend at least six months as a waiter/waitress just so they can see what it's like. I used to think $5 was an average tip. I've since learned that this is a jump-for-joy-and-cheer tip. Average tips are $3.
Since not everyone will have the opportunity to be a server, however, I'd like to pass on some of my learning. Let's also assume that everything I say refers to a good server. It's true that not all of them are (and believe me, I know this too!) But I am a good waitress. I'm always happy, attentive, keep your drinks filled, get you what you need on time, and I still have these complaints.
Second of all, you may not know it, but servers have an hourly wage of less than $3 an hour. When I got hired, I didn't think this was a big deal. I figured I'd at least make $5 off of each table, at least two tables an hour, we're doing great, right? Well... people aren't nearly so generous. Which brings me to my TIPS for you.
1) While there's no law (though there should be!), politeness dictates 15% tips for good service. If your server was exceptional, tip more! To the table of 4 with a bill of $42 that tipped me 2 bucks... there's just no excuse for that.
2) While we're on that, it's probably a good idea to tip at least a dollar for each person at the table. ESPECIALLY if those people sit in high chairs. This isn't about the total bill. This is about the amount of work your server is going to put into keeping you happy and cleaning up after you. So if you have two people and your bill is only $9, please tip more than $1. (I'm not making this up. I consistently get $1-2 tips.)
3) This is something I NEVER did before becoming a waitress, but if you get a To-Go order, tip the server! You might think they didn't do anything for you, but let me enlighten you: They answered the phone. They placed your order. They took time out from their tables to prepare your box, your condiments, your utensils. They took time out again to come to the register and ring you up when you showed up. They put your stuff in a bag, smiled and said, "Have a nice day!" A $1 tip will suffice here.
I've had nights where I only had four tables all night long. Sometimes we're slow, and I'm not the only waitress. If each of them tips me $2, well, you can do the math. Even if they tip $5, it's still not a ton of money. So if you liked your server, if they did a good job... show them your gratitude. They WILL remember it.
Good luck the next time you go out to eat!