Formal:
* Il faudrait que nous allions. (This is the most formal option and emphasizes the necessity of leaving.)
* Nous devrions partir. (This is slightly less formal than the first option.)
Informal:
* On devrait y aller. (This is a more casual way to say "we should go" and uses the impersonal "on".)
* Il faut qu'on y aille. (This is another informal option that emphasizes the need to go.)
* On peut y aller. (This is a very casual option, and implies a suggestion rather than a necessity.)
You could also use a more specific phrase depending on the situation, for example:
* Il est temps de partir. (It's time to leave.)
* On est en retard. (We are late.)
* J'ai faim. (I'm hungry.)
Remember to choose the phrase that best fits the context and your relationship with the person you are speaking to.