This 20 page packet very slowly walks students through relative pronouns starting with the basic qui, then qui, dont, où, lequel, combos of duquel/auquel, etc. and finally ce qui, ce que, ce dont, and ce à quoi. Every step is supported with examples and practice exercises. There are also side notes of helpful hints to recognize when you need to use various relative pronouns--for example, several expressions that use de and à. I've asked my students for feedback and they say this packet is easy to understand and they like that it moves slowly. I've seen great success in their ability to incorporate relative pronouns in their writing.
I use this with intermediate-mid students.