As for ESL/EFL beginner level learners ,vocabulary is the vital threshold of a strong basis that they have to lean on to learn English .On the other hand, the intermediate level learners have to burn the candle at its end to gain as much information as they can in an attempt to enlighten their labyrinths of achieving fluency.But the advanced level learners have to oxygenate the heart of the vocabulary stocks that they have been trying to store with idiomatic and specialized English to attain comprehensive knowledge of the English language.
Presently, there are many vocabulary activity books published by Cambridge University Press and Oxford University Press.These books or textbooks are gorgeously useful books.They hit the topics of the English of the quotidian life at different linguistic levels.And they include activities and exercises that vary in their gradual difficulty.If the ESL/EFL teachers and learners resort to these books, they might definitely make remarkable differences in regards to vocabulary acquisition.Here are a few examples of these books that the ESL/EFL teachers and learners can utilize:
1- Michael McCarthy & Felicity O‘Dell, Cambridge English vocabulary in use - elementary,Cambridge University Press,2012
2- Stuart Redman,English Vocabulary in Use, Cambridge University Press,2014
3- John Flowerdew & Matthew Peacock,The Specialised Vocabulary of English for Academic Purposes,Cambridge University Press,2012
4-Pauline Cullen,Cambridge Vocabulary for IELTS,Cambridge University Press,2015
5-Ruth Gairns & Stuart Redman,Oxford Word Skills: Oxford -Learner's Pocket ,Oxford University Press,2012
It might be useful if the the teacher introduces new vocabulary in every class in an indirect fashion. What is meant is that the in-class general discussions can be enriched through the new words that the teacher can give to their students in addition to those available in the textbooks.Of course this depends on the allotted time of the classes and the general responses of the learners.And the teacher can elaborate on the oral presentations delivered the learners with providing the learners with new words,expressions,idioms related to the discussed topics.Practically , these ideas can be applied upon any linguistic levels-elementary,intermediate and advanced.