Get a copy of "Sun Certified Programmer for Java" by Kathy Sierra and Bert Bates (other guide book are available, but I have not used them)
It has excellent coverage and tells you what you should concentrate on.
And whatever book/resource you get, make sure it is for the correct version of Java!
There's no way you can make the exam easier by asking other people about what topics they got more questions. All the topics on Sun's list of exam objectives are important, and you'll have to know them all.
Note that not everybody gets the exact same set of questions every time. Sun has a large set of questions, equally divided over the objectives, and gives you a certain selection of their large set of questions if you do the exam. The questions that you get will not be exactly the same as the questions someone else gets, but ofcourse the difficulty of all the questions that you get on your exam will be approximately the same as what someone else gets.