My first step to increase word power in English language is using cross words. You don't have to use unfamiliar words, just use the familiar one's correctly and based on your knowledge.
How to Increase Your Word Power by listening
If you listen to influencial speakers and some leaders alot, you'll automatically learn how to use words authoritatively without being arrogant or aggressive. Consistency is everything, learning how to increase your word power.
How to Increase Your Word Power using idioms
How many idioms can you recall now. Idioms help the speaker to be professional and reasonable even when the matter has no considerable sense. Idiomatic expression gets your listeners and readers brainstorm, while it keeps you on the verge of learning new words to alternate every said one.
How to Increase Your Word Power by adjustments
Replace a word you usually use with a synonym, just one every day. Do not miss a day with reading the thesaurus and the dictionary. For how to increase your word power, make sure you're using those exact words dialy in order to get them alive and functioning.