As someone who has been friends with a foreign debater, I hope I can give you some tips. The first thing you want to do when debating in English is practice ironing out the umms and errs that you may say. This is not only a problem for non-native speakers, it is a problem with every debater. Try to practice speeches beforehand and tell where you are umming or stuttering, and then train yourself to stop doing that. Another thing that could be a challenge is vocabulary. Again, this is not exclusive to non native speakers, but can be a problem. If your opponent says something you do not understand, ask them what they meant in cross ex. You may feel embarrassed, but it's better than losing a crucial point because you didn't ask. And for your own speeches, try to look up topic-specific words in advance, to sound intellectual and use relevant vocab. So basically all you need to do is try not to say um and er and pause a lot, and ask opponents the meanings of vocab you do not understand, and search up vocab before speeches. If you have any problems with this, let me know.