Language/Afrikaans/Grammar/Formal-vs-Informal-Imperatives

While the rule is that you should add moenie to an instruction (also called an imperative) in order to make it negative, a formal, more polite imperative will get an asseblief (“please”). As soon as you do this, there is another set of rules that apply. Have a look at the following: 

• Informal imperative: Moenie opstaan nie! / “Don’t stand up!”
• Formal imperative: Moet asseblief nie opstaan nie. / “Please don’t stand up.”

As you can see, when you add asseblief to the negative sentence, you need to: 

1. break the compound moenie into its component words moet and nie;
2. put the asseblief (“please”) between the moet and the nie; and
3. remember to add the final nie at the end! 

Here are some more examples using the same informal instructions as in exercise E.1, but now converted to formal imperatives.

Informal Imperative	Formal Imperative
Moenie later terug kom nie!	Moet asseblief nie later terugkom nie.
“Don’t come back later!”	“Please don’t come back later.”
Moenie daar kyk nie!	Moet asseblief nie daar kyk nie.
“Don’t look there!”	“Please don’t look there.”
Moenie weggaan nie!	Moet asseblief nie weggaan nie!
“Don’t go away!”	“Please don’t go away!”

Source

https://www.afrikaanspod101.com/blog/category/learn-afrikaans/afrikaans-grammar/#2