grammar - How to distinguish between う/よう of volition and suggestion?

Reading a lesson on 国語文法.com, I'm having difficulty telling 意志 from 勧誘.

E.g. 「今度こそ成績をあげよう。」 is stated is that of volition (意志). However, why can't it be "(I suggest you to) improve your grades!"?

Or the following example/exercise sentence: 彼の業績は評価しよう - is that the speaker's intention to evaluate 3rd party performance, or a suggestion to 2nd party to do that?

Or an image like this, is it the speaker's (猫さん's) intention or suggestion for the reader (a motivational image)?