Formal:
* Devrait: This is the most common and general way to say "should." It's used in both written and spoken French.
Informal:
* Doit: This is a more direct and forceful way to say "should," often used in a more informal setting. It's closer to "must" in English.
Other options:
* Il faudrait: This is a more polite way to suggest something, and translates to "it would be necessary" or "it would be good to."
* Il serait bon de: This is another way to suggest something, meaning "it would be good to."
* Il vaudrait mieux: This translates to "it would be better to" and is used when suggesting a preferable course of action.
Example:
* You should study harder. (Formal) -> Tu devrais étudier plus.
* You should go to bed early. (Informal) -> Tu dois te coucher tôt.
* We should go to the cinema. (Polite suggestion) -> Il faudrait aller au cinéma.
The best translation will depend on the specific context and the tone you want to convey.