What is your favorite PhotoShop Tip/Trick?

Hey,

Well I am sure a few of us have been using Photoshop for a fairly long time however I am sure we are all still learning and discovering new tools/options everyday. I recently stumbled across a very interesting feature which helped me dramatically, What I want to know is what is your favorite Photoshop Tip and hopefully other's may find your tip useful and use it in the future.

Mine personally is changing the curser using the 'Caps Lock' button especially when using the slice tool, as the knife curser is difficult to use.

So what is your favorite tip or tips?

Kind Regards,
BoxedPixels.