Which is correct between "not to do" or "do not do"
These usage make me confuse.
What is the difference?

And what is the difference between "Do practice this" and "Practice this" ?
Many thanks in advance (=

Question

Which is correct between "not to do" or "do not do"
These usage make me confuse.
What is the difference?

And what is the difference between "Do practice this" and "Practice this" ?
Many thanks in advance (=

Answer

We don't use "do" plus a verb in commands. It's simply wrong.

Practise this!

The teacher told us to practice this.

Answer

Thank you for your advice, I also learned like that, but I got an e-mail from my colleague "Do take very good care and stay in touch" 
Frequently I get these kind of email with "Do + Verb" so I've wondered.

Answer

'Practice this' is a command. 'Do practice this' is awkward and I can't imagine someone using it. You could say 'Do you practice this?' but this is a question.