The structure of CAT has changed quite a bit. Firstly, it shall be an online test this year instead of the written test which had been going on from time immemorial. Secondly, the number of questions has been reduced to 60-70 and the time duration has been cut short by 15 minutes (Initially, it had been a two and a half hour paper). Since this is the first time CAT is being conducted online, there will be a 15 min tutorial that will take place prior to the examination to make the aspirants familiar with the new pattern. Though the syllabus has not changed significantly, the decrease in the number of questions makes selective studying a highly inadvisable option.
In order to be well prepared for the test just be particular about going through the CAT papers of the last ten years. As for scoring remember that since there is negative marking, it is always better to rely on the accuracy rather than the number of questions answered.