Learn Hardcore Chinese: wǒ xiān kāi dēng, zài kàn shū. - I will turn on the light first, then read.

Yes. 我先开灯，然后看书 is fine. Nuance: 再 often feels like a plan or instruction; 然后 is a neutral “and then” in narratives. You can also say 先…, 然后再… to sound a bit softer in instructions.

Does 再 here mean “again”?

No. In 先…再…, 再 means “then/after that.” When 再 means “again,” it usually refers to future repetition, e.g., 我们明天再看书 (we’ll read again tomorrow). For past/current repetition, use 又, e.g., 我昨天又看了书。

Do I need to repeat the subject in the second clause?

No. If the subject is the same, it’s usually omitted: 我先开灯，(我)再看书。 If subjects differ, keep both: 我先开灯，你再看书。

Do I need a measure word before 书?

Not when you mean the general activity “read books” (看书). If you mean a specific book, add the classifier 本: 看一本书 (pronounced yì běn shū due to tone sandhi on 一).

What’s the difference between 看书, 读书, and 阅读?

看书: everyday, neutral “to read (books).”
读书: “to read” in a slightly more formal sense; also “to study/attend school” depending on context (e.g., 他在北京读书 = he studies in Beijing).
阅读: formal “to read/reading” (as an activity or skill), often in written or academic contexts.

What’s the difference between 开灯, 打开灯, and 把灯打开?

All can mean “turn on the light.” 开灯 is the most common and concise. 打开灯 explicitly highlights the action of switching it on. 把灯打开 uses the 把 structure to focus on the result (the light ends up on). To turn off: 关灯, or 把灯关上/关掉.

How do I express “read with the light on” as a state, not two steps?

Use the durative marker 着: 开着灯看书 = read with the light on (state). The original 我先开灯，再看书 emphasizes two consecutive actions.

How do I say this if the actions already happened? Where does 了 go?

Mark completion on the verbs: 我先把灯打开，然后看了会儿书。 You can use 再 in past narration too (我先开了灯，再看书), but 然后 is very common in past storytelling.

How do I say “Only after turning on the light will I read”?

Use 才: 开灯才看书 or 开了灯才看书. 才 adds the sense of “not until/only then.”

Can I use 后/以后 to say “after turning on the light, then read”?

Yes: 开灯后再看书 or 开灯以后再看书. Both are fine; 以后 can also mean “in the future,” but with a specific prior event like 开灯, it means “after.”

Is the comma necessary? And what about spaces?

A comma between clauses is standard and helps readability: 我先开灯，再看书。 Chinese normally has no spaces between words; spaces in learner materials are for teaching.

How do I make this a polite instruction?

Add 请 or 吧: 请先把灯打开，再看书。/ 我们先把灯打开，然后再看书吧。

What’s the classifier for 灯 if I want to specify one?

Use 盏: 一盏灯 (yì zhǎn dēng). In casual speech you might hear 一个灯, but 盏 is the standard, especially in writing. For bulbs, use 个 or 只 with 灯泡 (e.g., 一个/一只灯泡).

Can I drop 书 and just say 我先开灯，再看?

Only if context already makes the object clear (e.g., everyone knows you’re talking about reading). Otherwise 再看 is ambiguous (look again? watch again?), so keep 书 or specify another object.

Why not use 把 here? Is 我先把灯打开，再看书 better?

Both are correct. 把 highlights the affected object and the result state; it’s natural when you care about the light ending up on. Without 把 (我先开灯), the focus is simply on doing the action.

I confuse 再 and 在—they sound the same. Which one is used here?

Here it’s 再 (then/again). 在 means “at/in” or marks the progressive (在+V), e.g., 我在家; 我在看书。 They’re both pronounced zài (fourth tone) but have different meanings and characters.