shuāyá yǐhòu bié wàngjì xǐshǒu, ránhòu zài qù chī zǎocān.

In Chinese, the subject is often omitted when it is obvious from context.

Here, the sentence is giving an instruction, so the understood subject is 你:
（你）刷牙以后，别忘记洗手，然后再去吃早餐。

Adding 你 is possible, but it is not necessary.

以后 means after or later, and it usually comes after the word or phrase it relates to.

So:

• 刷牙以后 = after brushing your teeth
• 吃饭以后 = after eating
• 下课以后 = after class

This is different from English, where after usually comes before the action.

刷牙 is the normal everyday expression for brush one’s teeth.

A few notes:

• 牙 can refer collectively to teeth in casual speech
• 牙齿 is more formal or anatomical
• In daily Mandarin, people usually just say 刷牙

So 刷牙 is the natural phrase to learn and use.

It can mean both, depending on context.

• After a phrase or clause, it often means after
  • 刷牙以后 = after brushing your teeth
• By itself or in other contexts, it can mean later or in the future
  • 以后再说 = we’ll talk about it later

In this sentence, it clearly means after.

别 is a very common way to make a negative command: don’t...

So:

• 别忘记 = don’t forget

By contrast:

• 不忘记 sounds more like do not forget as a statement, not a natural command
• 不要忘记 is also correct and a little fuller/more explicit

In everyday speech, 别 is very common and natural.

Chinese usually does not need a separate word for to before another verb.

So:

• 忘记洗手 = forget to wash your hands

This is a common pattern:

• 忘记带手机 = forget to bring your phone
• 忘记关门 = forget to close the door

In Chinese, the verb can be followed directly by another verb phrase.

Chinese often leaves out possessive words like my, your, or his when the meaning is obvious.

So:

• 洗手 naturally means wash your hands here
• Saying 洗你的手 would sound unnecessary unless you are stressing whose hands

This kind of omission is very common in Mandarin.

They overlap, but they do not do exactly the same job.

• 然后 = then / after that
  It connects one step to the next.
• 再 = then / next / after that, and sometimes again
  It often marks the following action in a sequence.

So:

• 然后再去吃早餐 = and then go eat breakfast

Using both together sounds natural because:

• 然后 links the steps
• 再 emphasizes the next action in order

You could sometimes omit one of them, but together they sound smooth and idiomatic.

No. Here 再 means something like next or then in a sequence.

It does often mean again, but context matters.

In this sentence:

• 然后再去吃早餐 does not mean go eat breakfast again
• it means then go eat breakfast

So this is the sequencing use of 再, not the repetition use.

去 + verb often means go and do something, especially when there is an idea of moving somewhere to do it.

So:

• 去吃早餐 = go eat breakfast

This suggests going off to have breakfast, maybe to the kitchen, dining hall, cafeteria, etc.

If you just want to say the next action without the idea of going somewhere, you could say:

• 然后再吃早餐

Both are possible, but 去吃早餐 adds a sense of movement.

Yes, both are common.

• 早餐 = breakfast
• 吃早餐 = eat breakfast

Also very common:

• 早饭 = breakfast
• 吃早饭 = eat breakfast

Depending on region and speaking style, one may sound more natural than the other, but both are correct and widely understood.

Yes, absolutely.

• 刷牙以后 = after brushing your teeth
• 刷完牙以后 = after finishing brushing your teeth

Adding 完 emphasizes completion.

In this sentence, the completion is already understood from the sequence of actions, so 刷牙以后 is perfectly natural. But 刷完牙以后 is also very common.

Because this is an instruction, not a completed past event.

了 is often used for:

• completed actions
• change of state
• new situation

But here, the speaker is telling someone what to do in sequence, so 了 is not needed.

If you were describing what someone already did, 了 might appear in a different sentence.

Yes. Chinese usually presents actions in a logical time order.

This sentence is structured like this:

• 刷牙以后 = after brushing your teeth
• 别忘记洗手 = don’t forget to wash your hands
• 然后再去吃早餐 = then go eat breakfast

So the order is:

1. brushing teeth
2. washing hands
3. eating breakfast

This kind of action-by-action sequencing is very typical in Mandarin.

Yes. That is very common in Mandarin.

This sentence chains several actions smoothly:

• 刷牙以后
• 洗手
• 去吃早餐

Chinese often relies on:

• word order
• linking words like 然后
• context

instead of adding lots of little words like English does. That is why sentences like this can look compact but still be very natural in Chinese.