This a common question often asked by the students who just started the preparation of bank recruitment exams conducted by reputed public sector banks.

At the beginning of preparation of bank exam focus should be on the basics. Always remember, ignoring the importance of fundamentals may hurt your preparation at later stage so its better to remove dust from the basic concepts of Mathematics, Reasoning, Grammars etc.
        
Start from the Mathematics book of 9th and 10th and quickly remind basics like percentage, profit and loss, Interest rates averages, mensurations, Geometry, Number System etc.
         
For reasoning think about the puzzles you used to love playing during your childhood. Start playing Sudokoo, solve classic puzzles found in different books like relationship puzzles, number arrangement etc. You may think this type of question is irrelevant for bank exam. yes you are right, some of these questions are not relevant but remember it is the primary stage of preparation and your focus is on brushing up your basics. These question will act as a warm up for difficult question. It will create interest and open your mind.
         
For English section go through the grammar books of school days. Make a clear cut concept of basic things and try to find out the common grammatical errors people commit during writing or speaking. This will help you solve the common error questions asked in the English section of exam. Also read as much English as you can, improve your vocabulary by collecting word meanings, their antonyms, synonyms and also try to understand the sentence pattern used in the modern English. All these exercise will help you in the later and more serious stage of  exam preparation.

Remember for the success in the bank recruitment exam there is no alternative of practice. The more you practice the better score will you get. Solve as many question set as you can. Collect question banks of different bank exams and solve them daily. Try a join Mock Test series organized by many coaching institutes to evaluate your progress. Remember you have every thing that a winner have but you need to sharpen your skill to achieve your goal. After all Practice Makes a Perfect.