Sound out the words slowly that you are spelling. When we are speaking fast, we often drop certain sounds. Try saying the word by breaking it down by syllables, or syl-la-bles. This will help you hear each letter better.
As you read books, magazines, or articles online pay attention to words that are spelled irregularly or unusually. Keep a notebook where you can record such words and look them over each day until you remember their spellings.
Ask a friend or family member to quiz you once a week on the spellings of words in your notebook. You can see which words you still need to work on.
Look up spellings regularly in a dictionary or thesaurus. You can also "bookmark" a dictionary website to have as a reference for whenever you might need to use it.
Learn the origins of words along with the its roots. Knowing this can help you remember some of the correct spellings.
Make sure that you proofread everything you write and type. Many times we write or type so fast that we have many misspelled words. Many people rely heavily on the spellchecker function. But be aware that the spellchecker is not error proof. Make sure the spelling of the word is the correct and intended meaning. Many words in the English language sound the same but mean completely different things.
Think of creative tricks to remember the spellings of words. One classic example is 'The 'I' comes before 'E' except after 'C'. Make up word associations that are meaningful to you to help remember the correct spellings.