Read books and actively read them by making sure you understand what you've read and be aware of the author's sentence and paragraph structure. Copy(write) what you read by putting it in your own words. Do it over and over again and eventually, you'll improve your verbal skills. It's a slow process but that's what it takes.

Taking classes is not enough. It comes down to practice, practice and practice.

Also, keep a diary, it forces you to summarise your thoughts.