Starting about 10 weeks before the exam, we began meeting twice a week. Every meeting, we covered 1-4 items on the syllabus. (depending on the length and difficulty of the items as well as our level of familiarity with them) After covering all of the items, we divided the syllabus into three sections - Physical Design, Logic Synthesis and Formal Verification - and held a practice exam on each section. For each practice exam, each person in the study group would prepare two questions to ask others and also answer two questions from other people using the whiteboard. The week before the prelim, we asked students who had taken the exam before to prepare questions and administer mock prelims.
The following document contains each item in the above syllabus broken down into outline form. All of this information can be obtained by scanning the section headings from each paper and chapter, but I found it helpful to have a condensed view. The items in red are some of the important points from each of the subsections.
From my perspective, the most difficult part of the exam would be working out actual problem instances on the board. The main challenge being to remember the important parts of the algorithm while not wasting too much time on false starts. So, I came up with a number of topics from each syllabus item that could be the source of problem instances, and made sure I knew the basic idea behind solving each one.