Cut and move shortcuts
It's important to know the essential keyboard shortcuts for navigating and trimming layers in the layer panel, it's possible to move the timeline marker and layers around much faster and accurately without having to constantly grab the mouse.

Move the timeline marker to the in or out point of a layer

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Move the timeline marker to the next visible keyframe

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Trim the work area to the position of the timeline marker

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Move the in or out point of a layer

 

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In order to open a specific property of a layer, press the following key:

 

Opacity (transparency)

Rotation

Anchor Point

Position

Scale

Reveal all keyframed properties in selected layer

Reveal all changed properties (double tap)

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Trim the slected layers to the position of the timeline marker

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You can change which layer you have selected in the stacking order by combining the Cmd/Ctrl key with the up and down arrows

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Move the timeline marker one frame forwards or backwards

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Move the timeline marker 10 frames forwards or backwards

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Whilst a keyframe or a set of keyframes are selected, you can move it forwards or backwards in the timeline

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Same as with moving the marker, you can move the keyframes 10 frames forwards or backwards

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Resize and reposition a layer to match the width of the composition, whilst preserving the aspect ratio

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There is a very useful alternative to time remapping if you need to stretch or compress an animation, but want the keyframes to stay on that layer. Select a series of keyframes, hold Option/Alt and drag the beginning or end keyframe to stretch them out over time. After Effects tries to preserve the timings of keyframes, so as not to change the structure of the animation. This means that you may run into the problem of having a keyframe midway between two frames, in order to get the timeline marker to rest where you want it, you must drag the keyframe to the nearest frame. Beware this may distort the animation slightly, but often it is workable as it is never more than half a frame off.

These are the shortcuts I use the most, a complete list of keyboard shortcuts for After Effects can be found on the Adobe help website.