The secret knowledge of click board stacking is a third-eye opener: it opens a whole new (vertical) dimension, broadening the possibilities of what can be done with a single mikroBUS™ socket.
This microcontroller-projects post was written with the Microchip Express board in mind, but it doesn't matter. The rules and guidelines for stacking clicks on top each other can be applied to any mikroBUS™ socket.
The mechanical considerations are obvious, but worth pointing out.
As for the electrical, the short of it is this: click boards with an I2C interface are easiest to stack, you just have to pay attention to the value of the pull-up resistor. SPI clicks are not stackable, due to the colliding CS pins. Otherwise, if communication pins don't overlap, you can mix and match clicks with different interfaces.
Read the entire post on microcontroller-projects.com, bookmark it in your favorite note taking app, and start stacking.