"If" clauses

Hello everyone. After looking through various different sources, I can’t determine what to use after a clause that starts with “if”. Some say if must be followed by would/will, while others say it must not. They prefer using had. Can anyone please clarify?

If it’s possible/likely, you can use “will.” If it’s impossible/counterfactual/hypothetical/unlikely or if it’s in the past, you use “would.”

Yes: If I study harder, I will get a better grade.
Yes: If I had studied harder, I would have gotten a better grade.
Yes: If I were better at studying, I would get a better grade.

No: If I study harder, I would get a better grade.
No: If I had studied harder, I will get a better grade.
No: If I were better at studying, I will get a better grade.
@Thewildnorth96

Thank you