To clear aptitude test, GD and Interview (both technical and HR) you must be prepared well for the process. You should practice a lot aptitude and GD. you have to give demo interview to do well in campus interview process.
To clear aptitude test practice aptitude a lot. You may practice from the book of R S agarwal which is very popular book for aptitude. Try to practice aptitude question of previous recruitment process of the same company for which you will appear in recruitment process. Generally questions are repeated from the previous year paper. So solve previous year paper attentively. Then surely you will be able to clear aptitude test.
To clear GD round practice GD a lot. Improve your English communication skill. Try to appear in college GD competition or any other GD competition. In college there will be some GD session to make prepare for the campus interview for final year students. Try to attend this session. Then i think you will be able to clear the GD round. Now days there are so many companies removed the GD round in their recruitment process.
To clear interview round both technical and HR round you must be prepared well previously. To clear technical round you must have very good technical knowledge. Interviewer may ask you to tell two or three favorite subject of you. So study two or three subject very well so that you can answer any question from these subjects. For HR round prepare some common HR questions like introduce yourself, your strength/weakness, why you want to join this company etc. you must be prepare for these types of question and you have to answer properly. you must not copy the answer of these questions from other. In HR interview they may ask questions about the company details. so you must know all details about the company before appearing in recruitment process. Company details are available in their official website.