Spell-checkers can be helpful, but they will not catch all errors. To be sure that your spelling is correct, you must proofread your final draft yourself. The following suggestions for catching and correcting your spelling errors will help:
Proofread your writing carefully to catch transposed letters (becuase for because), omitted letters (becaus), and other careless errors (then for than). When you proofread for spelling, read the text backward, beginning with the last word. This strategy keeps you from reading for content and lets you focus on each word.
Check a good dictionary for any words you are uncertain about. When you are writing and doubt the spelling of a word, put a question mark by the word but wait to check it until you have finished drafting.
Keep a list of words you often misspell so that you can try to pinpoint your personal patterns. Although misspellings nearly always follow a pattern, you are not likely to misspell every word of a particular type, or you may spell the same word two different ways in the same essay.