There are a lot of books available in the market for aptitude preparation. But RS Aggarwal's Modern Approach to Verbal and Non Verbal Reasoning and Quantitative Aptitude and Logical Reasoning are considered as best books and also recommended by top educators. Apart from this, you can also follow Analytical Reasoning by MK Pandey, Arun Sharma's Quantitative Aptitude etc. Solving these booka can help you to understand the topics and these books has several exercises and questions to solve. Also you can solve aptitude questions online as there are lot of exercises available over the internet. Websites like Freshersworld can help you in this.