Avoid grammatical errors while speaking. Easier said than done, but it is really not that scary and difficult as it seems. Of course, you will not be able to eliminate all the mistakes. Even native speakers make them quite often. The point of this is avoiding the situation when you fall into silence because you are not sure how to use a given grammatical construction. Remember, there is always a way out. For example, when you do not feel good using Present Prefect, you may use Past Simple with time specification. So, instead of saying "I have been to Paris", you may say "I went to Paris some time ago". And remember the most important thing: do not panic!