The problem I had as a native English speaker was with calming the other person's nerves. Several people with whom I have spoken were so very nervous, even though they had a good command of English. This seems to be a common problem, and I know I had it myself when speaking a language I was studying. My best advice - don't be nervous! The English speaking person will be happy to help you if you want. And even if you do make grammatical mistakes, chances are you will be understood.