KeyLight is the easiest way to key out a foreground from a greenscreen in After Effects. Learn how to use the Keylight 1.2 Effect and the 3 main properties to modify, in order to obtain a perfect chroma key for your green screen: Screen Color, Screen balance, Clip Black and White.
The first property is the Screen Color. Push the ALT (or OPTION) button on the keyboard while clicking on the color picker, then look for a position on the screen that gives the best result on the status view (watch the video to see how to view the composition and the layer at the same time on the screen).
Do not forget to Subscribe to my youtube motion design channel, so you will not miss any of the weekly new tutorials
The second property is Screen balance: see this as three options: 5%, 50% and 95%. Take the one with the best result in the STATUS view.
The third and last is in reality a couple of properties: Clip Black and Clip White. Play with them: move them the fewer you can from their original value until you get the best result.
Using these properties, you can achieve most of the chroma keys, just keep in mind that this is not an exact science.. you need to experiment, and may be use masks to apply different keylight on different zones of the video.