Learn Hardcore Russian: Тебе стоит перечитать доклад ещё раз перед семинаром. - It’s worth rereading the report once again before the seminar.

Russian often expresses advice/necessity with an impersonal construction: кому? + стоит/надо/нужно + infinitive.
So тебе is dative = to you / for you, and the sentence literally frames it as For you, it’s worth (doing)… rather than You should….

What does стоит + infinitive mean here, and how strong is it?

стоить + infinitive means it’s worth doing / you should (it would be a good idea to). It’s usually softer than a strict command.
Compare:

Тебе стоит перечитать… = gentle recommendation
Тебе нужно/надо перечитать… = stronger necessity (you need to…)
Тебе следует перечитать… = more formal, “ought to”

Why is the verb перечитать (perfective) and not перечитывать (imperfective)?

перечитать is perfective because the speaker is recommending a single completed action—read it through again once, finishing the rereading.
перечитывать (imperfective) would suggest a process/habit or an ongoing repeated action, e.g. you should be rereading it (in general / repeatedly / as a process).