Hello

For cracking any banking exam like SPI PO/ IBPS PO/ NABARD Grade A etc, first you need to make a proper routine and follow it with full discipline
(discipline > motivation).

You are recommended to join any coaching as it will help tremendously in your preparation. But it is not compulsory and you can also do self study if you want to.

I would suggest seeing some videos available on Youtube about the toppers who cracked your dream exam so you can get an idea of what to do and what not do.

And last but not the least, practice practice practice.

Hope this answer helps! Thank You!!!