Accordingly you might be an eloquent speaker when it comes to your mother tongue, but expecting the same standards from yourself when speaking in a foreign language may not be very realistic. You often have to make the first impression as the best one in front of the audience.
When you learn a new word, try to memorize a couple of sentences that contain it as there might come a time when you can use one particular sentence with little, or no alteration at all. Most of us just memorize words by the heart with the synonym and we don’t know where to use it and how to use it.
Always learn to listen first before you speak. That is why God has given us two ears to listen more and one mouth to speak less. Speaking is always a spontaneous process and nothing prepares you for it better than actually doing it.