As a writer, I need to describe things from tropical sunset scenery to a villain's deepest darkest feelings, I work to hone my vocabulary skills. How?
Stop and let my senses record.
I work outdoors and have come to appreciate the amazing array of green hues I can see over a growing season. I have also worked in scorching heat and brutal humidity while being stalked by hordes of ravenous mosquitoes.
I used to note these things and keep on trucking. Now whenever I can, I stop. I will watch the red-tinted sun until it disappears under the horizon. I really listen to full fade of an ambulance's siren. I study the body language of a child with a new toy. I record as much as I can without allowing my inner voice to interrupt and do commentary. That way I build a bank of "clips" to use.
Let associative words attach themselves to emotional events.
I've given birth and discovered infidelity. I have been wracked by fear and rage, and filled to glowing with wonder, joy, and awe.
As soon as I can, I play back what I have "recorded," and let my feelings attach to the "clip." Some feelings are not immediately writable. Others are. Again, I am building a storehouse of future descriptions.
Use resources to expand my pool of words.
My Flip Dictionary thesaurus lists 72 words under the heading "Green." Dictionaries list antonyms. Children's encyclopedias have great pictures with captions and identifications.
News magazine reporters and columnists are often masters of the succinct description. Short stories are a treasure trove of good examples. Poets also play well with words. I read a variety of writing.
Nothing beats practice.