You can practise several activities at different levels about relative clauses and pronouns on the following links:
http://www.agendaweb.org/grammar/relative_pronouns_clauses-exercises.html
http://www.ego4u.com/en/cram-up/grammar/relative-clauses
If you want to listen to another way of explaning relative clauses, click on the following links:
http://www.youtube.com/watch?v=ASlCTRjHB7Y (Defining relative clauses)
http://www.youtube.com/watch?v=8vb9Yd5Kb44 (Non-defining relative clauses)
https://www.youtube.com/watch?v=-wJC9Pj5vCE (Object-Subject relative pronouns)