1. Mistake Type #1: Time Crunch
Out of all the questions you missed, how many of these "ran out of time" questions are there? If the majority of your missed questions happened because you were running low on time, you may have a time management issue.
 If you run out of time to answer all of the questions, continue answering questions, but mark the questions for which you needed the extra time. Afterwards, you can go back and categorize the questions you needed extra time for and sort them into the remaining three categories of errors.
How many questions did you get right with extra time, as compared to questions you answered correctly during test length? If your scaled scores differ by more than either 50 points on any section of the SAT, or by more than 4 points on any section of the ACT, then you have a time management issue.

4. Time strategies
One of the best strategies for students scoring in the 500 range is to just guess on the hardest questions. In fact, because of the way the SAT is scored, you can actually guess on up to 25% of the multiple choice questions and still get a 600.
How do you know which questions are the hardest ones? In Math, the questions at the end of each section are the most difficult. This means that, for instance, in the 20-question Math section, you should completely skip the last 4 questions. Focus the energy you would have spent on those questions on getting the other 16 correct.
Reading is a little trickier, since it includes lengthy reading passages, and the questions are not (for the most part) ordered by difficulty.
->When faced with a lengthy passage, read and mark-up the questions first. This way, you will already know the information you should be considering when reading the passage.
->Skim the passage on your first read-through. Sometimes, several lines of the passage will not have relevance to any of the following questions, so why spend extra time on a detailed read the first time through? If possible, try finishing the passage in 3 minutes or less.
->If you cannot answer a question in 30 seconds or less, guess "B" on it and move on. You won't have points taken off for incorrect answers, so if you guess the same answer choice for every answer you don't know, you should get it right about 25% of the time.
Overall, practice can help you get faster at taking the SAT/ACT, and the more high quality practice questions and tests you do and take, the more comfortable you'll be.

5. More time strategies Actions for a 700/31 Scorer:
If you're already scoring in the 700 range, and you know time management is not the issue, chances are you just need to up your speed (whether for one particular type of question or overall).
For every section, you should calculate your own time per question.
The key here is that during the test, if you find yourself spending more than your target time goal, you need to skip that question. You want to avoid getting sucked into wasting time on a question. On these points every question is worth the same point, and at your level every point counts. Therefore, your goal should be to answer as many questions correctly as possible.