Aptitude is not as difficult as many people fear. It is actually quite easy and it comes with practice. It is all basic Maths, English & Reasoning. Everyone knows the basics and can answer the questions. The challenge is answering the questions within the time limit which requires time management and decision making. If the test has negative marks then the best way to crack the test is picking the right questions to answer. Else the strategy should be attempting all questions within the time and getting most of it correct in a short span of time.
Preparation strategy :
Start early. Try taking some mock tests. Evaluate your ability and identify your strong and weak zones. Refer books like R.S. Agarwal or try out online tutorials for improving the weak zones. Refer websites like indiabix, etc. to try out questions of various companies. Practice on your weak areas constantly by taking more and more tests. This should actually help converting your weak areas into strong ones. Do this to convert each difficult topic to easy ones. Remember speed is of the essence here. Do this till you are confident in almost all areas and you eliminate almost all your weak zones.