1. Insist that your English as a Second Language students use an English-English pocket dictionary (see American Heritage) - often taken for granted by language instructors, this helpful bit of insistent advice will make a difference in their short and long-term interest in word study.
2. Recommend that ESL students keep a vocabulary log - writing down the words that are unfamiliar (or at least some of them) is a good first step in helping them find ways to use the pocket dictionary they will be carrying around.
3. Suggest English vocabulary building website - with so many ESL and native-speaker sites available on the internet, students should feel confident that 15 to 20 minutes of online word study will prove useful to them in the long run. See a4esl.org/q/h/vocabulary.html
4. Choose key "prefixes" for your students to study - by providing your language students with information about the meaning of a prefix such as "trans-", their ability to analyze and comprehend the essential characteristic of a list of words (transient, transistor, transit, transition, translate, etc).
5. Maintain an in-class vocabulary box - whenever a student asks a question about a specific word, write it down on a note card, have the class look it up in their dictionary, and place the card in a box. During successive class meetings, randomly choose words from the box to see who can recall the definition. This may work as a way to create tests as well.
6. Let students "tag" the classroom - for beginning students, provide note cards and scotch tape, tell them words for everything in the classroom (from common words like "desk" to others such as "door hinge" or "window sill." Write the name on the card and tape the card to the object. If possible, leave them up for a few days. Let the students review them before, during, and after class. Later, remove the cards and ask the students to place the their proper place.
7. Have students buy a word building book - for example, advanced students who are considering high-level academic study may want to consider buying a text from the Word Smart series, www.wordsmart.com/, which provides a free word of the day email option (hmm...1 word x 365 = 365 new words!)
And keep in mind that your students have a lot of experience studying new words, and they may be willing to share their favorite vocabulary building techniques with their classmates. By giving your students the opportunity to explain how they learn words, you will endorse the value of learning new words for everyone in your class.