"I will not study tomorrow."
Translation:मैं कल नहीं पढ़ूँगी।
It's not a rule.
The usual place for the verb is always right before the main verb. Eg: मैं नहीं पढ़ता हूँ।
Optionally, it can be placed right after the main verb Eg: मैं पढ़ता नहीं (हूँ)। This placement is used to emphasise the negation. You can do it with the future tense as well. It is more common in spoken form than in written form.