Ahhhhh ring styling. I love it.
People always ask would I do this or do that, and the answer is yes! I do it all. I love experimenting with stacking rings.
Some of my tried and true suggestions:
Mix shapes/lines - eg. Try one with straight sides, rounded, curved all worn together.
Switch the order - Sometimes switching the order of the bands will make them look completely different.
Mix thick and thin - The thin flat bands and twig rings have an amazing ability to give depth to a stack. It's amazing what a little texture will add to a stack.
Add a stack topper - Most people think that you should bookend rings so that there are two matching bands on either side of your main event ring. This can be lovely, but I also love two different bands on one side (or three) with a zinger on top. There is something incredibly balanced in the imbalance.
Don't be afraid to try things you wouldn't think are you. You just may surprise yourself.