Getting students to understand vocabulary through context is an important skill.
Prepare by choosing a passage for your student(s) to read. Underline words that you think will be challenging for the them and create a list of these words on a separate piece of paper or on the board.
Tell them to read it quickly the first time through. Then, have them read it through one more time and come up with definitions based on context for the underlined words.
If you are working with a group, pair students. They should compare definitions with their partners.
Share results as a class.
For more general reading strategies visit this blog post.