Hello dear student !
In order to prepare for any examination, you have to study in a smart way. The NABARD Grade A exam asks direct questions and difficulty level is averagely difficult and the seats are quite less.
First you need to study regularly and don't skip even a single day.
For the first 5 sections , the preparation is almost same as for Bank PO, etc. For GA refer to -
Any standard static GA booklet (such as Bankers Adda's )
Affaircloud 100 Questions monthly pocket booklet
GKtoday 250 Questions monthly pdf
Now, for 2 most important sections which are there in mains also,
You can refer to Edutap for this section.
you can refer to Edutap ESI static module, Union budget, Economic survey Vol. I , etc.
For English Descriptive Paper in Mains, you need to practice all the sections.
For interview, just read a national paper on Daily basis and be aware of your surrounding and all the developments amd changes.
Practice with online mock tests and practice ror every section as much as possible. Eat healthy and sleep properly.
Hope this will help you !
All the best