https://www.youtube.com/watch?v=V2IaOUjo8mE
This effect is super useful for patterns and is super duper easy if you know what all the transformations do.
First, obviously create a composition. Next, draw your shape.
Go to your shape layer, and you'll see the add button. Click on add, and in the drop down list, there will be something called "repeater." Click on it, and your shape will repeat.
Repeater will show up as an effect on your shape layer. If you click the drop down on this effect, you'll se a bunch of different alterations you can make on the effect.
Increasing the copies number will increase the number of shapes repeated. Changing the scale of the repeater doesn't change the scale of everything. It will be more of a gradual change. For example, if your initial shape is 100% and you change the scale of the repeater to 25%, each shape will get smaller until the first shape is 100% and the last shape is 25%.
A fun thing you can do now is to change the rotation. This does not rotate the shape but instead rotates the entire pattern. If you have shapes in a line with decreased scale, it'll create a fun twisting effect. You now have an animated spiral pattern in two minutes of work or less!