•  Most people believe that there is a very definite set of English rules which, when followed, will produce correct English. In reality, this is not true. A better question to ask is, "What is appropriate English?" The answer to that question depends on many things:

    1. The relationship of the speakers (e.g., good friends speak to each other different     than an employer speaks to employees)

    2. The situation in which the communication takes place (e.g., people have to provide     different kinds of information when talking over the telephone than when talking face-     to- face).

    3. The topic of the communication (e.g., you may speak differently in telling a joke     than you would in discussing a math principle), etc.

•  You should aim at teaching your students language that will help them achieve their goals appropriately. For example, they may want to be able to request help in a store. You would teach them to do it in such a way that they would get the help and that the people helping them would not think that they were rude, stupid, nor snobbish. Overall, instructors have a tendency to try to teach styles of English that are too formal for most of the situations their students will encounter

•  Try to avoid this fault. Contractions (I'm, he's, they'll) are always used except in very formal situations.