Watch verb endings. Walt Disney supply the voice of Mickey Mouse. Walt Disney supplied the voice of Mickey Mouse. Students needs time to study. Students need time to study.
Writers often drop -s endings for plurals when they are in a hurry to get ideas on paper.
When proofreading, look for marker words that introduce either plural or singular nouns. I look forward to most holidays. Spell check won't catch meaning or usage errors. Try reading through the essay with a ruler or a sheet of paper under the line, and examine each word carefully. Use a pen or pencil to mark off the syllables.