Saying should in Japanese?

Question:

I just want to clear this up for myself, how would I say "should..." in Japanese? I learned base ta + hou ga ii desu. And to say, "should not..." Base 1 + nai hou ga ii desu. How would I conjugate this? I was thinking:

ochitsuku- to calm down. So, ochitsuita hou ga ii desu. You should calm down.
Ochistuita hou ga ikatta- You should have calmed down, ect.
Conjugating the "ii" since the desu is just there for politeness because "ii" is an i- adjective. Same for "should not.." right?

I've also seen this translated to other ways, like njya? Is that even a word? I don't know, you guys tell me. Or beki? Theres probably a bunch of other ways too?


Help is much apprectiated, thank you very much. Every little bit helps. Thank you for your consideration in answering if you chosen too.

Answer:

When you heard the following (advices);

- ochituita houga ii (desu).
it sounds humble (less imperative ≒ 'd better)

*"～(verb/past tense) + houga ii" is almost an idiomatic expression ('d better ...), regardless of whether you have other options to compare with.

- ochitsuka nakereba dame desu, ochitsuiku beki desu
it sounds more imperative (= should/ have to/ must/ need to)

*....(verb/ imperfective form)-nakutewa dame desu yo, ...(verb/attributive form) -beki da/desu.
*In colloquial: "....(verb/imperfective form)-nakya dame" is wedely used.
e.g. benkyou shi-nakya dame dayo, hon o yoma-nakya dame yo
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Ochistuita hou ga ikatta --> grammatically incorrect
--> ochitsuite iru beki deshita "you should have been calm."

should not .... "...(verb/attributive form) -beki dewa nai"
e.g. ima sonna koto o iu beki dewa nai ("you shouldn't say such things at the moment"