There are a few things you can do to reduce careless mistakes. The first strategy I would recommend is always double checking your answers at the end of each section. Do all of your answers make logical sense? Careless mistakes often become glaringly obvious upon a second glance at each question.
If you make mistakes on Math problems, I would try circling or underlining the value you need to find so that you can stay focused throughout your calculations. Sometimes people solve for the wrong value by accident because they're too wrapped up in the math and forget to go back to the original question.
You can also try quickly rereading the question along with your answer after you've made a decision. Make sure your logic is sound and you understood the question correctly the first time. If you answered a question very quickly without thinking too much about it, you might have misinterpreted what it was asking.
It's hard for me to give more specific advice because I don't know where you make most of your careless mistakes. If there are some sections that give you more trouble than others, you should investigate why that might be. Are you nervous? Do you tend to rush on certain sections? A deep analysis of your mistakes and revamping of test-taking strategies can help you to eliminate careless errors.
To answer your second question, I would say that repeating practice tests isn't super helpful. You're showing that you've memorized the correct answers, not that you've necessarily gained new knowledge that you'll be able to use on future exams whose questions are unfamiliar. I'd advise you to get another review book that has lots of new practice materials if you're set on further improving your score.
I also want to add that you shouldn't expend too much energy aiming for a 35 if a 33 is already above average for the schools where you plan on applying. In that case, your time is better spent improving the other components of your application.