Lately, there have been a lot of submissions that have contained errors that should have been caught before upload. These include errors that a simple spell check or careful final read-through would have served to eliminate.
For an editor, this is especially frustrating. Ultimately, it is the responsibility of the author to check his or her work for easily corrected errors. While your word processing program's spell check cannot be relied upon to catch every error, it should still be used. Spell check may help you to catch typos that your eye has skipped over time and time again.
For problems with homophones or wrong word usage that spell check won't solve, a final read-through is essential. If you don't feel confident that your article is error free, read the article aloud to yourself (reading out loud take considerably longer than reading by sight only--it will force you to slow down and listen to your words) or ask someone else to proofread your work for you.