Joining a institute or preparing at home totally depends on you. 

In order to crack CLAT you must be aware of syllabus and exam pattern and level of questions. You should refer previous year questions papers. If you have any doubt try to solve it. You must make a time schedule and work according to it which helps you to cover all the topics of all the subjects. 

You can also make your important notes which will help you in revision. You can also solve complete mock test to know your strength and weakness. 

All the Best!!