The best way to prepare for the first multiple choice question section of the TSA is by doing past paper questions timed. The time pressure is the hardest part of the paper - you will have less than two minutes to answer each question - so the most important thing is to make sure that you can answer all 50 questions in the given 90 minutes. Most people perform worse on average on the problem-solving rather than critical thinking questions, but this may not be the case for you. Work out which you do better or worse on on average when marking your past papers, and concentrate on those questions when practising. If you run out of past papers, there are many TSA practice books available with sample questions that you could use.