wǎnshang wǒ chángcháng xiān xǐzǎo, zài shuìjiào.

晚上 is a time word meaning in the evening / at night. In Chinese, time words very often appear near the beginning of the sentence, before the subject or right after it.

So these are both natural:

• 晚上我常常先洗澡，再睡觉。
• 我晚上常常先洗澡，再睡觉。

Putting 晚上 first helps set the time frame right away: As for the evening...

No. Chinese usually does not need a preposition like in before time words such as:

• 今天 = today
• 明天 = tomorrow
• 晚上 = in the evening

So English says in the evening, but Chinese simply says 晚上.

常常 means often.

In this sentence, it comes before the verb phrase:

• 我常常先洗澡，再睡觉。
• I often first take a shower/bath, then sleep.

This is a common position for frequency words in Chinese: after the subject and before the main action.

A very simple pattern is:

subject + frequency word + verb

For example:

• 我常常去那儿。 = I often go there.
• 他常常看书。 = He often reads.

Both can mean often / frequently, and in many cases they are interchangeable.

• 常常 is very common in everyday speech and often feels a little more conversational.
• 经常 can also mean frequently and is slightly broader in use.

In this sentence, either would sound natural:

• 晚上我常常先洗澡，再睡觉。
• 晚上我经常先洗澡，再睡觉。

For a beginner, it is enough to remember that both usually mean often.

先...再... means first... then...

It is used to show sequence:

• 先洗澡，再睡觉。
• First take a bath/shower, then go to sleep.

This is a very common Chinese pattern.

Examples:

• 先吃饭，再学习。
  First eat, then study.

• 先回家，再做作业。
  First go home, then do homework.

So in your sentence, 先 marks the first action, and 再 introduces the next one.

Because 先 and 再 are marking the order of the actions.

• 先洗澡 = first take a bath/shower
• 再睡觉 = then sleep / then go to bed

Chinese often puts these sequencing words directly before the verb they modify.

Because 常常 describes how frequently the whole routine happens, while 先 describes the order inside that routine.

So the meaning is:

• 常常 = often
• 先...再... = first...then...

Together:

我常常先洗澡，再睡觉。
I often first shower/bathe, then sleep.

If you change the order, it can sound unnatural or change the focus.

It can mean either bathe or shower, depending on context.

Literally, 洗澡 is the general idea of washing oneself / bathing. In modern everyday speech, it very often refers to taking a shower, but it can also be translated as take a bath.

So in this sentence, a natural English translation could be:

• In the evening, I often take a shower first, then go to bed.
• In the evening, I often bathe first, then sleep.

The exact translation depends on context.

It can mean both, depending on context.

• 睡觉 literally means to sleep
• In many everyday sentences, it is also used like go to bed

In this sentence, the most natural English translation is often:

• then go to bed or
• then sleep

Because the sentence describes an evening routine, go to bed sounds especially natural.

Because the subject is already clear.

Chinese often avoids repeating the subject when it stays the same:

• 晚上我常常先洗澡，再睡觉。

The full meaning is understood as:

• 晚上我常常先洗澡，再（我）睡觉。

But repeating 我 would sound unnecessary here.

This is very common in Chinese.

The comma is not absolutely required, but it is very natural and helpful.

Both are possible:

• 晚上我常常先洗澡，再睡觉。
• 晚上我常常先洗澡再睡觉。

The comma makes the two-step sequence clearer, especially for learners.

Yes. That is also natural.

Both of these work:

• 晚上我常常先洗澡，再睡觉。
• 我晚上常常先洗澡，再睡觉。

Chinese time words are flexible in this position. Putting 晚上 first gives slightly more emphasis to the time setting.

Yes, that is possible, but it changes the nuance a little.

• 先洗澡，再睡觉 = first bathe/shower, then sleep
• 先去洗澡，再去睡觉 = first go take a bath/shower, then go to sleep/go to bed

The version without 去 is simpler and more direct. The version with 去 emphasizes going to do the action.

In everyday speech, the shorter sentence is very natural.

It describes a habit or usual routine, because of 常常 (often).

Without 常常, it could describe a simple sequence:

• 晚上我先洗澡，再睡觉。
• In the evening, I first shower, then go to bed.

With 常常, it clearly means this happens often.

Sometimes yes, if the context already makes the subject clear.

For example, in conversation:

• 晚上常常先洗澡，再睡觉。

This could be understood as (I) often shower first, then go to bed at night, if everyone already knows you are talking about yourself.

But as a complete standalone sentence for learners, keeping 我 is clearer and more natural.

A useful way to see it is:

time + subject + frequency word + first action + then action

So this sentence is:

• 晚上 = time
• 我 = subject
• 常常 = frequency word
• 先洗澡 = first action
• 再睡觉 = second action

Pattern:

时间 + 主语 + 常常/经常 + 先 + 动作1， 再 + 动作2

Example:

• 早上我常常先喝咖啡，再工作。
  In the morning, I often drink coffee first, then work.