I have been working my way through some excellent tutorials by Tara Roys on how to work with Apophysis. What makes them a cut above all the other tutorials I’ve struggled through is her clear, mathematically-based explanations of the processes involved. All of the other tutorials I’ve looked at explain how to do a particular technique, but they fail to explain why.
Here are some examples of very basic fractals I made using the same two(!) transforms, and just two variations. The only difference between them is the scale change of one transform. Amazing.