Feed Your Brain
What you put into your body will help what you ouput (test results as well as your overall GPA!). About an hour before you start your cram session, feed your brain with foods that help to promote concentration and cell turnover. Bananas, walnuts and spinach are all good options. See the resource link below for more ideas. Be sure to snack throughout your cram session to stay full, that way you will also stay focused.
Focus on the Big Picture
Pull out your notes and your textbook that you've used that semester. Especially with a final exam (as opposed to a midterm), the semester has come full circle so you should easily be able to pick out the main themes and ideas. The same theory would go for math related problems since in most cases you build upon what you learn throughout the semester. Focus on those points. Retake notes in an abbreviated format on these sections to help build yourself a concise outline. Use this to study from.
Don't Waste Time
Don't focus on what you know you won't be able to learn before the final. Sometimes some concepts - unless you are sure they will wind up on the exam - aren't worth the time and effort you'll need to put forth in order to understand them in time. To get the best test results or GPA in the shortest amount of time, focusing on strengthening what you already know.
Sleep
If you can't afford a full 8 hours of rest, do what you can. If you have finals exams all day, you'll need more sleep. If you only have one exam with a break in between, try to get a solid 4 hours before the exam and then take a nap later. After about 4 hours sleep, you'll wake up for the exam feeling pretty alert and well-rested, but it won't last long. You'll need to rest up if you have another exam that day.