Have a look at previous navigators (
http://www.disneycruiselineblog.com has loads on it).
Also try not to schedule everything but have an idea of the things you really want to do. I tend to write a list of must-dos to make sure I at least do a few of them. Every cruise it changes (on no. 9 now) and every cruise I don't get it all done but it gives me ideas to look out for.
Take a highlighter! Every night (or in the port on the first day) you get your navigator and what I did was take a few minutes first thing in the morning to go through and look for things I thought I might want to go to. I then highlighted them and was set for the day. Just made it a bit easier to keep track fo things and spot them on there. Still missed some great things but at least I spotted some too.
I took small sandwich bags (like ziplock ones in the US) so that I could put cookies and sandwiches in the fridge during the day to then eat as a snack if I got hungry that night. Although the fridges are more like coolboxes they worked for things like this that would normally last a little while. I also put drinks in there (lemonade) so I had something to drink at night as well. Just be careful with anything that needs to be stored at set temperatures as its hard to tell how good they are.