I like to take care of hard workers. My only pet peeve is when you hand the waiter/waitress the check and payment, so many ask "Do you need change?" They should always say "I will be right back with your change" at that point you say "No the rest is for you".
Technically for good service you tip 20% of the bill, excluding tax and alcoholic beverages. If the service is good, I at least give 20% of the total including tax and beverages. If I use a debit card to pay the bill, the tip is in cash. If I am not wrong, the IRS assumes the waiter gets at least 10%. So If I give them 20% in cash, they won't take such a hit.
When I was a Cop, my job went after establishments who gave Cops "a break" on the bill. So this practice was almost non existant. I personally never liked getting a "break", to me it was embarrassing, considering that I was making a decent living, compared to them. There was a diner in a really bad area I worked. The food was so good and was about the only decent place to eat. I would go to pay the manager at the cash register. He would cut the bill in half. For example, a $20 dollar bill was $10. I wouldn't say a word, pay the $10 and then give the waitress $12, so in essence I payed my bill, although I guess I was saving $2 on the tip, instead of my total being $24.
I never had to feel bad about eating there a few times a week, the manager was happy and the waitress received what she deserved.