Hi, Samir. Usually if I’m speaking to a basic speaker it seems better for their learning to just let them speak rather than interrupting the flow of the conversation, then offer a few suggestions when there is a pause. When people are beginners you can’t possibly correct all their errors, and it would be very discouraging for them. It is easier to receive correction when you give a compliment first. I often ask, do you mind if I make a suggestion? Once you get to know them better you’ll develop a rapport and corrections will become a matter of course.

For intermediate level speakers, I just repeat what they said the correct way. For instance, If they say, I speak to him yesterday, I may say, you spoke to him yesterday? They will usually correct themselves on the spot. If it’s a more complicated correction I’ll type it so they can read the words. This is what I prefer also.

I find people pretty responsive when my facial expression and tone of voice convey support. A little praise goes a long way.  “I see you’ve been practicing the past tense!”

If someone is really annoyed by corrections, I would question their suitability as a language partner.

I like to write down the corrections and also prefer if my partner writes down the corrections. This way we can both review the corrections after the session. But I would only correct major mistakes, unless the partners wants to have everything corrected, because it can be very discouraging to receive too many corrections.

Depending on the mistake I wouldn’t always write it down but using the riggt form in my reply. Let’s say the partner says: “I have two childs.” I might reply: “Ah, you have two children? I have three children.”

I don't have a language exchange partner yet, so I did not have any experience in terms of corrections, especially on a voice chat. However, I have a few tips for that. The first is: Always let a student finish a sentence. Do not stop him right in the middle, he'll forget what he wanted to say. I suppose that to some people, I'll have to let even come to a particular point the way to which is a bunch of phrases. If a person wants written notes,  we'll compile right during his speech till he comes to a sense point.  I think this scheme will work with pre-intermidiate and higher. What to do with beginners till intermediate. I suppose their speech will be less correct and if I interrupt them every time we won't have a conversation. I think that they shall be corrected step by step. My task as a "teacher" will be to find out the main problem he's struggling with now and explain it right after the common conversation. Again written notes will be helpful for us both.

If a person does not want to be corrected, do not correct him or her, at least do not correct grammar. Correct only vocabulary.

I personally get upset when I see loads of mistakes corrected by my teacher. Afterwards, when I understand why he corrected me I feel joyful ahahaha