It completely depends. Two people can study the same amount, and one will get a B or C on a test while the other will ace it. The bottom line is: how good are you at memorizing facts and spitting them out on a test? If you want to be at the top of your class, the bottom line is: how disciplined are you at making yourself memorize useless facts and trivia that will get you a few extra points on the exam? Naturally the people who memorize the best and work the hardest will be at the top, not just the people who work the hardest.
Another consideration is how your school determines rank. My 1st year I thought my rank was based on percentages, so I went balls to the wall and studied 24/7 to get the highest possible percentage on every test. Then I found out rank was purely based on GPA, so I hit the brakes a little and got low 90s in every class. Figure this out so you can plan accordingly. It was more stressful skating around the grade border, though.
The difference between an A and a B in dental school is pretty big, and it involves lots of minutiae. Some people who scored B's or even C's on tests in dental school grasped the information better than I did because they looked at the big picture and were thinking in terms of clinical application rather than "I must memorize every fact and number possible."
Also, is your class a bunch of gunners? That will make your life harder if you're trying to be at the top.