He speaks English good. - This is a mistake even native English speakers commonly make. The adverb 'well' should be used instead of the adjective 'good' to describe how someone does something. This is just one of a number of common English mistakes. Others include understanding the differences between since and for, and understanding the use of a few / few and a little / little. These mistakes and more can be found on the common mistakes page. Each mistake is explained with a follow-up quiz to check your understanding.