"You should exercise more."
よ makes this more light-hearted like offering advice to a friend. Such as: "that's just my opinion, you know"
I think yo is necessary to tell that you're talking to a person instead of talking about yourself
It makes it less direct and more of a suggestion, i.e. "if you gave up smoking, it would be good" instead of "you should give up smoking". Non-past is okay, though.
They didn't even include an exclamation mark or anything to let you know to use yo
でしょう is used to mean "Let's" which really does not work with a sentence making a suggestion. I can't even figure out how I would word that in English.
Whoops nvm my post above. でしょう is more of a "probably" than "let's" (since its not modifying a verb, but a noun). That would soften the suggestion, to be more of something like "You should probably exercise more. "
It could mean "I should..." or "one should..." as well, wouldn't it? It's all about the context, isn't it?
Yeah it all depends on what is said before this sentence. For example, if 毎日私は食べすぎだ is said, the context of this would be you, and if 毎日あなたは食べすぎだ is said, the context of this would be I.