There's no simple answer to this, but remember that when you are speaking a foreign language, you are doing the hard work. When you are speaking, pay attention to the other person's expression to see if they are following you- if you think they don't understand, then repeat what you have said in a different way. Use plenty of body language- that often helps. If you can't find words, try to get the listener to help you with them. Remember that when you are trying to speak in a foreign language and are not fluent, use the listener as a resource and for help.