Is the same case as in English. One=Uno You=Tú Uno debe comer un desayuno grande y una pequeña cena. O Tú debes desayunar bien y cenar poco (Tú) is more common nowadays, but (Uno) is still very normal and popular.

Non-native speaker here: The third person singular reflexive is often used: Se dice = it is said Se come = people eat From Spanishdict.com: ¿Se come bien en este restaurante? Do people eat well in this restaurant? ¿Se come bien en este restaurante? Is the food good in this restaurant?

"One" as a subject can be translated as ( el que/quien ) ( uno) ( se ) El que / quien come bien, vive mejor. Uno no sabe lo que vendrá. Se requiere mucha ayuda.

Thanks, Bill. I'm sure I'll eventually get there in my course book but for now is the construct in point 3 used as a passive or is there also a passive voice in Spanish?

Other folks have mentioned all the common alternatives that I know about: 1. Using "uno", equivalent to using "one" in English 2. Using "tú" or "usted", equivalent to using "you" in English 3. Using an impersonal "se" construction, which is the pronoun "se" plus a verb in third-person singular verb, with no other expressed or implied subject