Buy a writing journal or create a document on your computer just for writing exercises. Write about your day, movies or television shows you've seen, books you've read, or stories you've created.
After you finish a writing exercise, correct misspelled words or words. If using a computer, use the spell check function. Are there any adjectives you find yourself using over and over? Look them up in your thesaurus and find new words to use. Make a comprehensive list of these new words and write them on flash cards.
Check out a variety of books from the library. Choose books in your reading comfort level and a level higher. Literary classics are good for learning vocabulary. Not only are they great representatives of storytelling, but they are also referenced in everyday culture. Examples include Mary Shelly's "Frankenstein," Mark Twain's "Huckleberry Finn" and Charles Dicken's "A Tale of Two Cities." The website literature.org/authors has many classics available free of charge.
Read nonfiction books that grab your attention. Maybe you want to design a bird feeder or cook Spanish cuisine. These books will keep your attention and help you expand your vocabulary.
Read books with specific exercises for improving your spelling and reading. ESL, or English as a second language, books are wonderful for building your skills. "Practice Makes Perfect" by Jean Bates, "Writing Better English" by Ed Swick and "ESL Intermediate/Advanced Writing" by Steven Michael Gras are good tools.
Visit websites that offer free online spelling and reading exercises (see Resources).