According to the American Heritage Word Frequency Book, the following words are the most common words in English.
1. The
2. Of
3. And
4. A
5. To
6. In
7. Is
8. You
9. That
10. It
11. He
12. For
These might be the most common words, but they're also the ones that will probably give you the most trouble, knowing them is one thing, knowing how to use them quite another.
Size can be deceptive.