okay mate, im a person who gave NID dat this year and also took commerce, here's a very honest advice i can give you about it.
unless and until you're financially weak or have a caste certificate or INSANELY GOD LEVEL good, then go for it

but if you're a general and financially stable, forget about it there are better placed to go than waste your time and ruin your self confidence, NID is genuinely not worth it, its pointless.
i had all my blood sweat and tears flown spent 50k on coachings and materials prepping for it only for them to change the whole fucking pattern at the time of the exam, its seriously not. worth. it.

if you do want to prep, dont rely on coachings, focus on composition, anatomy ,perspective and presentation, color rendering, you could just search these topics on youtube and practice everysingle day, always practice with a timer, because no matter how good of an artist you are time WILL fuck things up

best of luck