If you are a really ambitious learner of English, the sentence that you probably most dread to hear from a stranger is "Your English is very good!" This may sound like a compliment, but in fact it means that the person you are talking to has realized that English is not your first language. It is possible that your grammar, pronunciation and intonation are perfect, but you still don't sound like a native speaker. This may be because you don't use the many of the idioms and phrasal verbs that are so prevalent in spoken English, or because you don't use question tags.
Question tags are an important part of everyday communication and perform many different functions. For example, they can be used to get a conversation started or keep it moving; they can soften an order to do something or they can be a more polite way to request information.
Apart from the difficulty of knowing when to use question tags appropriately, the non-native speaker has to learn how to form them and how to say them. The general rule is that you finish a positive statement with a negative tag, and vice versa, using the main verb (if there is no auxiliary) or the first auxiliary verb (if there is an auxiliary).
How you say the tag depends on the function of the tag. The following sentence, when seen written down, is ambiguous.
This could be a genuine question; i.e. I don't know if you have seen him or not and I want you to tell me. (In this case the tag would be stressed and said with rising intonation). Or it could confirming what I know to be true and expecting an response like: "No, he hasn't been here all day." (In which case, the tag would not be stressed, and it would be said with falling intonation.)
See if you can finish the following sentences with the correct question tag. The first ones are relatively easy, but then they get more difficult!
If all this seems rather difficult, then maybe you should learn French or German instead. In those languages there is only one question tag, that can be used in almost all circumstances!
[A reader of this page pointed out that the term right is common in American English. So you could say: She's pretty, right?]