How do you save favorite effects in a "favorites" folder in After Effects?

You also have this folder in the Effects & Presets panel. As soon as you want to save a favorite animation, effect or group of effects, you only need to select them inside the timeline panel and go to Animation > Save animation preset. Also you can drag and drop this selection over the Effects & presets panel and you will have the same result. After Effects will prompt you to create a FFX. Once you save the file you can access to this preset from the Effects and Presets Panel.