1. Don't write alot
    The correct form is a lot
  2. Don't confuse the contraction "it's" with the possessive "its"
    One is correctly it is and the other is a possible pronoun
  3. Don't use loose when you mean lose
    When you lose your money, it is lost. However when you loosen your knot, it is not so tight and therefore loose. A tooth often becomes loose before you lose it
  4. Don't confuse possessive forms with plural forms
    Companies vs company's slogan
  5. Don't confuse their, they're, and there
    Their is possessive, they're is contraction of they are, and there is a location
  6. Don't confuse affect with effect
    Affect is a verb (I.e. The weather affects your mood) effect is a noun (I.e. The weather has an effect on your mood)
  7. Don't confuse then and than
    Then is used for time and than is used for comparison.