Check out the consolidated advice thread. I'll repost my advice, but lots of other people talk about what worked for them too.
I spent five minutes going through the exam at the start and ranking the problems that I knew or could do really quickly, ones I thought I could solve, and ones I knew I wouldn't get, would need a lot of time, or didn't understand at first glance. Then I started going through all the easy ones (I actually started at the end and worked forward since I was at the back of the booklet anyways). I marked everything on the answer sheet as I answered. Anything I had to come back to, I circled the number. Then I worked my way though all the middle-tier problems, then had about 45 minutes at the end to address the handful I had ranked the hardest. I attempted all of them and made educated guesses. This worked out really well for me.
Like VTEnviro said, the questions are grouped by topic so I was still generally doing all of the same types of problems at once, but I didn't waste time spinning my wheels on things I wouldn't be able to solve. Also, I think answering the ones I knew how to do first was a huge confidence boost, and that certainly didn't hurt anything. I swear the first few problems on both the morning and afternoon are the hardest ones in the whole booklet!