Writing exercises are a good tool to help one hone their skills. The following exercises are great for helping a writer determine which words serve no useful purpose in a sentence or paragraph.
Select a subject and write a descriptive paragraph. Once the paragraph is written, go over it word for word, marking out any unnecessary words. Run a word count on the unrevised paragraph and another after revision. You may be amazed at the difference.
Read newspaper or magazine articles in search of unnecessary words and content. Take one paragraph from the article and see if you can improve it. There may be no excess. You may not be able to improve it. Even so, if you pay close attention to how other writers keep their words and descriptions down to size, it will soon be second nature for you to do the same.