I’ve found a summary of Relative Clauses online which provides excellent revision for English students who are having difficulty with them. (Did you notice that there were two Relative Clauses in the previous sentence?)
Even students who understand the rules should revise them now and then so that they don’t forget! This site provides clear examples of different types of Relative Clauses and several tests so you can check your knowledge.
Practise using Relative Clauses by singing songs by Shania Twain and Shakira.