After Effects has hundreds of documented shortcuts, and the ones that matter are the property reveal keys and the keyframe shortcuts, because those are what you press dozens of times per composition. The Adobe keymap uses Ctrl on Windows and Cmd on macOS; the letters are the same on both.
Composition 7
Layers 8
Keyframes 8
Playback 4
Effects 3
Keyframes without the stopwatch
Alt + Shift + P, Alt + Shift + R, Alt + Shift + S and Alt + Shift + T add a keyframe for position, rotation, scale and opacity on the selected layer at the current time, which is faster than twirling the layer open and clicking the stopwatch. Once keyframes exist, J and K jump the playhead to the previous and next visible keyframe. U reveals every animated property on the selected layers and UU — pressing it twice quickly — reveals every property that differs from its default, which is the fastest way to audit what someone changed.
Layers and composition
Ctrl + Y makes a new solid and Ctrl + Alt + Y reopens its settings; Ctrl + Shift + C pre-composes the selected layers, and Ctrl + Shift + D splits a layer at the playhead. [ and ] trim the layer's in and out points to the current time, while Ctrl + ] raises a layer one step in the stack and Ctrl + [ lowers it. Ctrl + K opens Composition Settings, where duration and frame rate live.
Previewing
Space plays and pauses, and 0 (Numpad) starts a RAM preview that renders frames into memory before playback; in current versions both run through the same preview engine but the numpad key defaults to a full-speed cached preview. . on the numpad previews audio only from the playhead, and Alt + . previews the work area. Page Up and Page Down step one frame — the opposite direction from what the key names suggest to some people, since Page Down goes forward in time.
Frequently asked questions
What does pressing U twice do?
U reveals animated properties on the selected layer. UU reveals every property that has been changed from its default, animated or not.
How do I add a keyframe without opening the layer?
Select the layer and press Alt + Shift + P (position), R (rotation), S (scale) or T (opacity).
How do I split a layer at the playhead?
Ctrl + Shift + D. The original keeps the part before the playhead and a new layer holds the part after it.
Why does my RAM preview stop early?
It plays only the frames that fit in memory. Lower the preview resolution, or shorten the work area and preview it with Alt + . on the numpad.