Write about things that made you feel happy, memories you make, inspiring incidents or may be even that adventurous dream of yours where you flew on winged horses and tasted that candy cloud.
Though seems weird it actually works. Eventually you’ll be able to use appropriate words and you could even track your progress.
Try writing stories, songs or poems… remember all these efforts will never go in vain but will only make you more fluent and believe me your logical thinking too will be drastically enhanced