how should I improve my knowledge technically to be placed in good company? which exams will be applicable to pursue my higher studies?

Interviewers generally evaluate a candidate based on his/her response (thinking process approach to unknown problems. So they look for problem solving skills as well, in addition to experience.
Knowledge of data structures and Algorithms are must along with decent coding skills. In addition, knowledge of computer Networks and object oriented programming can come in handy as well. do start learning Algorithms and data structures. Try to solve as many problem as you can.