SSB is all about personality, aptitude and not the testing of knowledge or physical strength. Because all other traits can be trained only if you have the right psychology. If you have the power to influence and command others without any ego or attitude problem then you are in. There are ain 15 OLQs that are theoretically defined.  Even in daily life, we can easily tell if one can handle tough situations without any stress. You might have even observed people in daily life that some people are dominant, others may talk illogical and unnecessarily, others may get hyper during certain situations. On the other hand, you might have encountered people with perfect charm and elegance. It is all about personality.  To clear SSB, just start introspecting life and see what all can be improved in your personality on a daily basis. Observe yourself, observe others, and even observe what things can be improved.

Coming to the selection process, a personal interview is about your thought, your consistency and your ability to defend your stance. If an officer sees potential in you, he may cross-question you and you got to defend yourself. Even in daily life, you don’t get to know a person unless you talk to the person about things that matter.

Now Defense force is about group and team. So the certain ground task is to be performed. If you are dominant or unable to express your ideas then it's a big deal for you. Make sure even in daily life make sure you be a leader.

Coming to Psychology, they are about the subconscious mind. Since 5 days are not enough to actually test your capability or performance in a real-life war, they test the subconscious mind. If you have negative thoughts or a tendency to get stress or a potential suicidal, then it can be tested there.

SSB doesn't require any preparation, but life does. Prepare for life. Know yourself, know how to improve. Know the right, know the wrong, only then you will be able to defend yourself in the personal interview.