How should I divide up my time during the exam?

Use the number of marks as a guide - if the paper is worth 80 marks and you're given 1.5 hours, I'd allocate 1 minute per mark which would give you 10 minutes (or more if you're quick) to check over your answers at the end. It's very important to leave time to check through your working if you can because this is often when you'll find small mistakes that could bring your grade down!
As well as planning out your time, if you're spending longer on a question than you've got time for it's important to move on and come back to the question you're struggling with at the end. There's no sense wasting your time on a question you aren't sure how to do when you could be getting the marks for the others in the meantime!