I worked in the service industry for years when I was younger, and most people have no idea how important tips are, regardless of how much. That being said, here are some etiquette things regarding tips
1. Don't leave a tip with any denomination less than 25 cents. Pennies, nickles and dimes are incredibly annoying. Servers go home with a huge heavy pocket full of change they have to convert somewhere
2. If the service was just basic, nothing out of the ordinary, tip what you normally tip. Be it 10%, 15% or 20% (15-20 is becoming standard in Canada, but I would only give 20 if it was GOOD service, 15 for adequate, 10 for... brought me my food, wasn't an asshole)
3. If you happen to be tipping low, follow #1 at least but just leave it on the table. Giving a shitty tip personally to a waiter will be embarassing for both of you. Their face will tell it all
4. If you had exceptional service, make it a point to do what was posted earlier, get the attention of your server, or even go to the bar/kitchen/server-area and ask "Is Kelly there?" or whoever, then personally give them the tip and point out specific things that made your visit so enjoyable.
Almost all the time servers have shitty days. Customers are more inclined to gripe and complain about every single little thing and blame it all on the server when in reality, the cook/kitchen screws up. The bartender screws up, someone else screws up. You're shooting the messenger. Don't get me wrong, when I go out to a restaurant I expect to get everything I asked for exactly the way I asked for it because that is their job, and everyone should have those expectations. It's just that servers get way more negative feedback and attitude than praise. One kind guesture or nice word will make their entire night
Waitresses are called servers, as are waiters.
5. for any tips, you should get a bill with some sort of folder-book thing - put the tip inside there. Most times, leave the tip on the table but not close to the edge of the table or highly visible. People steal tips all the time if they're easy to walk by and snatch. E.g. if you tip $10, put the 10 dollar bill under a cup in the middle of the table