Hi Celine, when I do language exchanges we decide together on how long we both will speak each language. I've done 45 min each or 30 min each, it depends on how much time you both have and how comfortable you are in speaking the language.
It's better not to mix both languages because you'd easily fall back on the language you know better, plus it confuses your brain as it's receiving information in one language and is supposed to answer in a different one.
About corrections, it's better to take breaks every 5/10 minutes or so in the conversation then correct mistakes. If you wait until the end you'll need to be taking notes while the person is speaking and that may not help them to concentrate if they see you are writing down things all the time.
A few more tips:
- It's hard to find people who are really committed to improving on the long-term, often as soon as life gets busy your partner will naturally want to focus on his own work/family. Reserve a specific moment each week so that there's no risk of forgetting the appointment or any trouble with picking a date.
- Look for exchange partners who have a few similar interests so that the conversation will not wither away after the first few meetings.
- If you can, it's much more fun to meet in person with a language exchange so that you can actually do something together like going for a walk in the park, visit a museum or any other activity you both enjoy.
- Finally, try to find someone who has a similar level to yours so that you can have conversations in a similar manner and learn from each other how to correct grammar mistakes or not feel frustrated about each other's level.
Hope this helps, enjoy your time speaking French!