Speaking With Native Speakers...

Hi! You know that 1 .It is very different to talk with native speakers and than just someone from a different country.simply foreigners. If your partner isn't not a native speaker it is really easier to converse because he may not speak not so fast as fast.  , without a lot of idioms and much more clear. Your understanding becomes better since not many idioms are used.  Opposite situation with native speaker. This is especially so with my new customers. As for me it can be my new customer. How do you think, how can ask him to speak not fast, more clear in politely way? And what is the politely form for expression:"Repeat please, i have lagged behind to understand..." I have to be polite and have to ask them in a professional way to ask them slow down.  The best way is to ask them to repeat what they said.  Usually I ask them in this way, "Can you please repeat?  My oral Englis isn't great.  I have a difficult time catching up with your words."

If you please - correct my text and give me an advice.
Thanks!

1.  Don't use such phrases such as, "you know"...  you are insulting your readers.  Of course they don't know and that's why you write and explain in this article.  "Remember this..."  This sounds like you are from some superior position than your reader. You are writing an personal essay.  Your writing must not come across as condesending or from authority.  Ticks people off.

Speaking with native speakers...

Hi! As you you know, that it is very different to talk with native speakers compared to with simply foreigners. If your partner isn't a native speaker it is actually really easier, because he would speak not so less quickly, avoid a lot of idioms and be much more clear. It's the opposite situation with native speakers. As for me, he/she could be my new customer. What do you think - how can I ask him not to speak so fast, and speak more clearly, in a politely way? Also, what are the politely forms of expression, eg. "Repeat please, i have lagged behind to understand..." I'll give some examples below. :)

If you could, please - correct my text and give me some advice.
Thanks!

Just a quick grammar note: politely describes the action. To ask politely, to speak politely.  Polite describes the thing: a polite person, a polite request.

Some useful phrases:

"Could you repeat that, please? I'm having difficulty in following."

"I'm sorry, I didn't catch that."

"Could you speak more slowly, please? I missed what you said the first time."

"I don't quite follow you. Could you say that again?"

Without Could you... please?, the sentence sounds like a command. Not so polite. :)

Hope that helps!