Learn Hardcore Japanese: mensetu no setumeisyo wo yonde kara, situmon wo kangaete oite yokatta desu. - After reading the interview information sheet, I’m glad I had thought of some questions in advance.

面接 = interview
説明書 = instruction sheet / manual
面接の説明書 = “interview instruction sheet” → the explanation about the interview or for the interview

So here の works like the English noun–noun connection:

面接の説明書 ≈ “interview manual” / “manual for the interview”

You could also see similar patterns like:

日本語の先生 = Japanese language teacher
車の説明書 = car manual (manual for a car)

Using の is the normal way to link two nouns in this kind of “A of B / B for A” relationship.

Why is から used after 読んで? Doesn’t から usually mean “because”?

から has two main uses:

“because/since” (reason)
“after (doing something)” (sequence in time)

In 読んでから, it’s the second meaning:

読んでから = after reading (it)

Structure:

Vて + から = after doing V

Examples:

ご飯を食べてから、勉強します。
= I’ll study after eating.
日本に来てから、寿司が好きになりました。
= After coming to Japan, I came to like sushi.

So in this sentence:

面接の説明書を読んでから、
= After reading the interview instructions,

it sets the time order of events, not a reason.

What is the difference between 〜てから and 〜たあとで? Could I say 読んだあとで instead of 読んでから?

Both 〜てから and 〜たあとで can mean “after doing ~”, and 読んだあとで is grammatically fine here.

Subtle differences:

〜てから
- Often feels a bit more sequential, like Step 1 → Step 2.
- Slight nuance of “once I did A, I (then) did B.”
〜たあとで
- More neutral, just “after ~”.
- Often used for a clearer time reference (after lunch, after work, etc.).

In your sentence:

面接の説明書を読んでから、質問を考えておいてよかったです。
面接の説明書を読んだあとで、質問を考えておいてよかったです。

Both are natural; 読んでから sounds slightly more “first I did this, then that” in a smooth sequence, which fits well here.

What does 考えておいて mean? How is 〜ておく different from just using 考える in past tense?

〜ておく has the idea of doing something in advance / leaving something in a prepared state for later.

考える = to think (about), to consider
考えておく = to think (about it) in advance / ahead of time

So:

質問を考えました。
= I thought of questions. (simple past statement)
質問を考えておきました。
= I thought of questions in advance (for some later situation).

In your sentence:

質問を考えておいてよかったです。
= I’m glad I had thought of the questions beforehand.

It implies that thinking about the questions before the actual interview turned out to be beneficial later.

Could I say 質問を考えてよかったです without おいて? What changes?

Yes, 質問を考えてよかったです is grammatically correct, but the nuance is a little different.

質問を考えてよかったです
- “I’m glad I thought of questions.”
- Just happy that you did the act of thinking of questions.
質問を考えておいてよかったです
- “I’m glad I had prepared questions (in advance).”
- Emphasizes that you did it ahead of time and that this preparation turned out to be useful later (e.g., during the interview).

So 〜ておく adds a clear “preparation” nuance that the basic 〜て form doesn’t have.

Why is よかった in the past tense if I’m talking about how I feel now?

よかった is the past form of いい (good).

The pattern Vてよかった literally means:

“It was good that I did V.”

In English, we normally say:

“I’m glad (that) I did V.”

So:

質問を考えておいてよかったです。
= I’m glad I (had) prepared some questions.

The logic is:

The action (考えておく) happened in the past.
Looking back now, you think “that was a good thing”.
So you use past よかった to say “it turned out to be good that ~”.

This is a very common pattern:

早く家に帰ってよかったです。
= I’m glad I went home early.
日本語を勉強してよかったです。
= I’m glad I studied Japanese.

Why is it よかったです and not よかったでした?

よかったです is the polite form of よかった, and it is the natural, correct expression.
よかったでした is grammatically possible but sounds unnatural or overly stiff in most everyday contexts.

Think of:

いい → よい (formal) → よかった (past)
Add です to make it polite: よかったです

So:

❌ よかったでした (sounds off in normal conversation)
✅ よかったです (normal polite speech)

Use 〜てよかったです as the standard pattern:

会えてよかったです。 = I’m glad I could meet you.
天気がよくてよかったです。 = I’m glad the weather was good.

Who is the subject in this sentence? Why is there no 私 or 僕?

In Japanese, the subject or topic is often omitted when it’s clear from context.

In your sentence:

面接の説明書を読んでから、質問を考えておいてよかったです。

The speaker is talking about their own experience, so the understood subject is “I”:

(私は) 面接の説明書を読んでから、質問を考えておいてよかったです。
= (As for me,) after reading the interview manual, I’m glad I had prepared some questions.

Saying 私は is not wrong, but Japanese avoids repeating pronouns if they’re obvious. It sounds more natural without them unless you need emphasis or to avoid ambiguity.

Why is the object marker を used twice: 説明書を and 質問を?

Because there are two different verbs with two different direct objects:

説明書を読んでから
- 説明書 = object
- 読む = verb
質問を考えておいてよかったです
- 質問 = object
- 考える = verb

Each verb needs its own direct object marked with を.

This is a common pattern when you have multiple clauses joined with 〜て or 〜てから:

本を読んで、メールを書きました。
ご飯を食べて、宿題をしました。

Is the comma after から necessary? Does it change the meaning?

The comma after から is not grammatically required, but it is stylistically common and helpful:

面接の説明書を読んでから、質問を考えておいてよかったです。
面接の説明書を読んでから質問を考えておいてよかったです。

Both are correct and have the same meaning.

The comma simply makes the sentence easier to read by visually separating:

Clause 1: 面接の説明書を読んでから
Clause 2: 質問を考えておいてよかったです

Japanese punctuation is flexible; commas are mainly for clarity and rhythm, not strict grammar.

Could this sentence also mean “Because I read the interview instructions, it was good that I had prepared questions”?

In practice, in この文の形, 読んでから is read as “after reading”, not as “because I read”.

Vてから = almost always “after doing V”
Vたから = “because (I) did V” (past + から)

So:

読んでから → after reading
読んだから → because I read

Your sentence uses 読んでから (te-form + から), so the natural interpretation is:

After reading the interview instructions, I was glad I had prepared some questions.

If you wanted a clear “because” meaning, you would use 読んだから or rephrase the sentence.