Read Strunk and White's "The Elements of Style" cover to cover and consult it frequently. It is a source of grammar and style for many professional writers.
Learn to cite according to Modern Language Association and American Psychological Association style. Visit your school or public library to find credible resources and practice citation. Stay up to date with changes in popular styles by subscribing to their official websites or linking to their Facebook pages.
Use Google to your advantage by using simple search terms to find sources. For example, "weather Cancun" yields more precise results than "weather report for Cancun Mexico." Also, search specific cites by entering your search term followed by "site:website." For example, "MLA Style site:MLA.org."
Read critically acclaimed essays from established essayists, such as Joan Didion. Imitation is the first step all writers take before settling into a style of their own. Don't be afraid of imitating your favorite essayists, as your own style will begin to emerge out of good habits learned from other writers.
Strengthen your lede. The lede is the introductory paragraph telling the reader the "what" and the "why" of the essay. Write better ledes by starting from a general idea and working to a specific idea with clear phrasing and concise sentence structure.
Explore ideas in-depth by by forming a thesis that evaluates or synthesizes information rather than reports.
Write actively with nouns and verbs. Avoid awkward and tedious sentence structure by writing symmetrically and varying the length of sentences.
Revise the essay until it is like a well-groomed shrub. The revision should trim the fat of the essay so that its main idea is free of unnecessary embellishments.