Minimal pairs are pairs of words that have one phonemic change between them. For example: "ship" and "sheep". You can use activities with minimal pairs to help students recognize the minor differences between English sounds. This can help their comprehension and pronunciation skills.
Search on-line for ESL MINIMAL PAIRS for activities and worksheets. Check out the great pronunciation resources on the Okanagan University web-page at http://international.ouc.bc.ca/pronunciation/
This can be a fun addition to any tutoring session. Chose the sounds that you have noticed as challenging for your learner.