This may be your full time job, or you may just be trying to pay your way through school. Either way, you may not love it. You might, but in my experience, waiting tables in a means to an end, not the end goal. However, there are a few things that you should be aware of.
When I come into a restaurant, it's for a specific reason. It's a little celebration. It may just be me going out with my friends, but I don't do that very often and it's special to me. It may just be an ordinary work day for you, but to me it's special.
When I come into a restaurant, the last thing I want is to be judged for what I'm ordering. If you're commenting on my order choices, it's probably not welcome. A small comment, such as "good choice", or "those are delicious" is one thing. But do not comment on how much someone is ordering.
I went out for desert after a gymnastics competition yesterday, and ordered the most massive desert on the menu. It was a chocolate sauce with brownie and cheesecake bits, all enveloped in pizza dough, sprinkled with powdered sugar, chocolate sauce and served with whipped cream.
Now, in my waitresses defense, she didn't know that I struggled with bulimia. But after being shocked that I ordered it for myself, and not too share, she went on to tell me that she's the only person she's ever seen finish the desert. Talk about triggering!
Again, there's no reason to assume that your guests have eating disorders. But they might. And this may be a super challenging thing for them to do. Eating in front of others. And now you're putting more attention on it, and it might make your guest feel extremely uncomfortable.
We also live in a society, where eating a lot is viewed as "bad" and self control and salads are seen as "good". I by no means agree with this, society is quite distorted, but there's now way that the comments that were made to me last night would make anyone feel good, even if they didn't have an eating disorder.
So please, next time you're waiting tables. Don't comment on your guest's appetite, ability or inability to finish their plate. Frankly, it's none of your damn business.