One way to teach context clues is to give each student a printout of an encyclopedia entry and then ask them to write down any difficult words they find in the passages they read. Once the students are finished writing down the words, you can ask them to reread that same passage and look for context clues that give them the meanings of the difficult words they found. Finally, let the students write what they think the words' meanings are and then give them a dictionary to verify the meanings of those words.
Another idea for teaching context clues is to give each student a short story and then have them write four main themes of the stories based on what they've been taught about context clues. After each student finishes writing what he thinks are the main themes, have him stand in front of the class and discuss his story's main theme. Also, give students feedback on their analyses and suggest ways they can improve in future assignments.
You can also assign each student a set of 10 sentences about a certain topic, but the catch is that each sentence will have two difficult words in them. The students will have to guess what these words mean by locating context clues in the sentences. When the students finish their assignments, they'll each present their answers for the sentences in front of the class, and you can critique their efforts.
Another idea for teaching context clues is to give each student a short poem and ask them to determine the main subject of the poem based on what they learned about context clues. Then have each student discuss their poem and ask them how they used context clues to get their meanings. If some of their answers are incorrect, mention why and give suggestions on how to improve on their interpretation.