Read through the paper line-by-line. A ruler can help you focus on one line at a time, if you are proofreading a print copy. You can also read the essay backwards -- meaning, read the last sentence first, instead of beginning with the first sentence. That way the content of the paper will not distract you.
Check for spelling errors. If your paper is typed, a word processor with a spell check can help you with this. However, keep in mind spell checks do not always catch words you have spelled correctly but are the wrong words. For example, spell checks will not notice if you meant to write "from" but wrote "form" instead, as "form" is also a word.
Find the subject and verb in every sentence. Ensure they all agree in count. That means if a subject is singular, the verb must be singular as well.
Conjugate verbs in the proper tense. One-time events that happen and finish at a particular time require the simple tense. Events that occur while another event happens take the progressive tense. When explaining when one event happened in relation to another event, use the perfect tenses.
Look for run-on sentences, comma splices and sentence fragments. Correct these errors so that they are complete sentences that are punctuated accurately. A run-on sentence contains two independent clauses joined together without a semicolon or a comma and conjunction. Comma splices connect two independent clauses with a comma. Sentence fragments are dependent clauses that stand by themselves.
Hunt for missing words. When typing or writing fast you may have skipped over little words such as "the" or "a." You can easily find these by reading your paper aloud. Add these words as necessary.
Change incorrect prepositions, such as "composed in," which should actually read "composed of."