One thing at least is certain: you should avoid using the generic pronoun "one" which is felt as very rare, formal, even archaic in modern English. It often has moralistic undertones and basically means "a decent person", never a group of (more or less unidentified) people. In other words: the pronoun exists but is seldom used.
Example: "One has to obey one’s parents" (a strict nanny would say to a child). Here, "one" just means "a decent child".
You should also avoid "we" – keep it for you and your friends, you and your family, i.e. a group of people whom you are part of, and whom you know. There is no generic/impersonal "we" in English. Whenever the referent is totally unknown, or vague and generic to the extreme ("any person", "all people"), the passive voice is generally chosen.
Example: « On dit que le pain fait grossir » : "Bread is said/believed to make you fat" (One says that/it is said that bread makes you fat are both improper phrasings). Here « on » is not a specific category of people; it is anyone, anybody.
Another example: « On m’a volé mon téléphone dans le métro » : "My phone was stolen from me in the subway" (here you don’t know who « on » is, hence the passive voice).
Whenever « on » is used to posit the existence of something, i.e. to express the fact that something exists, "there + be" is generally used.
Example: « On entendit une immense explosion à l’extérieur » : "There was a loud explosion outside".
Another example: « On aperçut un éclair lumineux à l’horizon » : "There was a bright flash of lightning on the horizon".
LAST BUT NOT LEAST, whenever « on » refers to an agent that is vague but not completely unknown, some generic pronoun is used rather than the passive voice.
Example: « On mange beaucoup de riz en Chine » : "They eat a lot of rice in China" ("a lot of rice is eaten in China" would sound awkward, or at least very formal/technical).
Another example: « On aime beaucoup le vin rouge en France » : "We/they love red wine here in France" (here, « on » means the broad category of French citizens, of which the speaker is either part ("we") or not part, hence "they"). In these examples, the agent is broad and vague but it does correspond to a specific group that you could define and name. What this lesson has shown you is that there is no direct and unique equivalent of « on » in English; here, context is paramount, and you should always ask yourself what ‘on’ refers to.
