Here is one idea.
If you can wear a wrist watch or there is a clock in the room, pace yourself by it. That way you won't spend too much time agonizing over any one question. This is really helpful for essay tests. It's usually pretty quick calculation. Two hours for exam with X number of questions which you realistically think you can answer X minutes each. For short answer and essay questions, You don't need it perfect, but you do need it complete.
When time runs out on a particular question, move on. Don't beat yourself up. Just move on to the next question. The axiom that your first answer is usually correct is accurate. If you have time left over skim written answers first for grammar, etc.
For math and science that have formulas or rules to memorize, when you first get the test write them out on the back of the test. Basically brain dump all that stuff so have room to think on the test questions. It will save time when you need the quadratic equation or the third law of thermodynamics some time later in the test.
I hope some of this helps.