Hi Sarahmob... so glad you enjoyed your cruise. Tipping is always a much brought up topic! Generally speaking we Brits only tip when we get exceptional service BUT there are certain countries where tips are expected because they form part of the pay (US for example).
My mantra is little but often which was advised to do by an American friend! Something I have stuck to and it seems to work! No matter where we have been, we tip on the first day, drip feed and like the proverbial carrot and donkey...we never fail to get exceptional treatment! Of COURSE , it isn't compulsory in the majority of places BUT if it gets you what you want for little money, then why not?
Doesn't mean you get especially bad treatment if you don't tip btw but people being people, they gel towards those who do tip! Done it myself working in a bar!