To clear the tests, find out the question paper pattern of each company from the net (
www.freshershome.com etc) Often even questions are repeated. Some good books are R S Aggarwal ( aptitude, reasoning) , Barron's GRE (English vocab)
Only few companies have GD's . anyway have a good understanding of the current issues. they asked me my opinion about the kerala assembly elections in my TCS interview prettty deeply.
prepare the answers to list of common questions. some of these are
---------introduce urself
---------why shud v choose u?
---------y did u appear for our job/company? (say the strenghts they boast in their website)
--------strengths and weaknesses?
----------were do u see urself in 5 yrs?(PROJECT MANAGER is a good answer)
--------will u relocate to our remote location in Africa (SAY YES)
---------if I tell u , u r nt intellignt will u agree (say NO politely and explain why you thing u r intellignt)
---etc.
Whenever you go to the interview, try to smile .. dont reveal that u r tense. dont put ur elbows on table.. dont play with ur pen. dont try to be arrogant.. u'll get through.
further detail : Please refer