Etiquette: Just be nice!  It will help immensely if you know at least some basic Slovak.  Don't expect that everyone must know English!  Avoid being loud on the street; people will give you strange looks. 

Tipping: Locals will tend to round to the next 10.  Foreigners tend to tip more, and people know that, but no need to go overboard.  10 percent is polite.  When paying, each waiter tends to have his or her own wallet.  Tell them the total you intend to pay if you need change and they will return the remainder from the larger bill you give them.  When paying by credit card, you should tell the waiter when you ask for the bill, and also tell the total amount with tip.  Otherwise you are expected to leave the tip in cash.  There is no 'tip' line there.