-You can select several layers at the same time by holding Ctrl or shift.
-If you hold Alt and click on the eyes of a layer to change its visibility all the layers visivility of the proyect change except for the one you click on.
This can be useful when you have for example 20 or more layers and you want to see only the layer you are currently working on, so normally you would click 19 times on the other layers eyes but you can avoid that with this tip

Its very simple but i guess i didnt realize about them before because ive been very busy animating.