Students who say they never or hardly ever used dictionaries often speak English well but usually write poorly, because they make many mistakes. The students who use dictionaries most do not learn especially well either. The ones who look up every word do not read fast. Therefore they do not have time to read much .Those who use small two-language dictionaries have the worst problems. Their dictionaries often give one or two words as a translation of English. But one English word has many English translations in Chinese. The most successful students are those who use large college edition dictionaries with about 100,000 words but do not use them often, When they are reading these students first try to get the general idea and understand the new words from the context  .Then they read and use the dictionary to look up only key words that they still do not understand. They use dictionaries more for writing. Also if they think a noun might have an unusual plural form or a verb might have an unusual past form, they check these in a dictionary. The writer tends to think that_.
Choose a good dictionary, and you will succeed in learning English Dictionaries are not necessary to the students who learn English it is very important for the students to use good dictionaries properly . using dictionaries very often can't help to improve writing