1.Go through interview experience
First, spend few minutes on reading interview experience posted by candidates who already attended interview in that company.
My suggestion is Indiabix, Freshersworld,Glassdoor,Quora and some other sites.
If you read many reviews about their experience, you can get some idea on how the questions are asked and which part you have to concentrate in all rounds of interview.
2.Start your preparation
Now start your preparation with Aptitude. From previous step analysis, you might have noted which topic to be given importance and make some time to that particular topic.
Then start preparing on Reasoning topics also.
On the other hand, spend some time for Group discussion and HR interview because in the both rounds good communication is important.
Take some of the repeated topics and prepare it well so that you can be confident enough to speak in interview.
For technical interview mostly they will ask question from area of interest and from your subjects(From basic to latest trends). Hence,you can crack it well if you brush up little.