This lack of clarity could indicate the need for a better format, a different use of language, or a different style. Having a friend proofread the piece will provide a fresh point of view of the work and may also detect additional mistakes in facts or grammar. Writing is about communicating ideas, and those ideas are ultimately conveyed by the language you use. Thus, correct use of vocabulary, proper spelling, appropriate punctuation, and clear grammar are necessary. Invest in a good dictionary, an even better thesaurus, and an English guide.
Writing is like all other skills - it takes discipline and practice to improve.
Using these suggestions will give you the tools you need to ensure more effective and concise writing.