I’ve been working as a waitress for about three and a half months now, and it’s kind of making me start to lose faith in humanity. During my one of my shifts, despite being sickeningly pleasant to everyone I encountered and providing my best service, I had two tables leave no tip at all and one that left me $3 on an $80 bill. This is a problem.

In case you didn’t know, tipped employees in Michigan are paid only $3.10 an hour; that’s up this September from $2.65. And this hourly wage always goes entirely to taxes so, day to day, waitresses live entirely off their tips.

Well technically, your restaurant is required to make sure that your tips amount to at least minimum wage, which seems like a pretty good failsafe. However, employers determine this by looking at the server’s reported tips for the entire two-week pay period. This means that, if a waitress makes $20 in five hours of work one day and make $70 in five hours the next, she won’t receive any extra money on her paycheck.

In addition, waitresses have to do a fair amount of side work while they’re in their restaurant, and during this time, they’re not making tips. This ranges greatly from restaurant to restaurant, but when it’s all said and done, this work (stuff like rolling silverware, cutting lemons, sweeping floors) probably amounts to an hour of my time each shift, which I am paid $3.10 for.

So when servers are actually on the floor, every table counts because every dollar counts when rent is due.

Lately, I’ve been trying to figure out whether people genuinely don’t know these figures and have never been taught tipping etiquette, or if they’re just jerks. I’d like to think it’s the former. So here’s a quick cheat sheet for you.

I know you might have grown up hearing that you should tip 10%. I did, too. But the going rate is 20% for good service. If you can’t afford to tip well, you can’t afford to go to a restaurant with a wait staff.

But if you go to Applebee’s or Peppino’s and get a half-off appetizer and an ice water, this doesn’t give you a license to leave a fifty cent tip because that’s 20%. If your bill is low, you should probably still be tipping at least $2, and a bit more for great service.

Also, make sure your expectations for your waitress are reasonable. She’s a person, not a robot. If she forgets to bring you your Coke with no ice or isn’t at your table the second you need her, look around you. It’s likely you’ll see her carrying other people’s food out of the kitchen or that she’s swamped with several other tables. Be patient.

Lastly: your tipping habits can either make or break a waitress’s night. You may likely be part of the reason that she goes home in a good mood, singing to the radio, or part of the reason she sits in the parking lot crying in her car.

Don’t screw it up.