Grease Pencil

When going for a 2D grease pencil animation start with a 2D animation file instead of a default file.

Drawing with the Grease pencil actually draws in the 3D space, but looks at it through the camera. Adjusting either the camera or the shapes (scale) can modify what and how you see on the canvas.

Using a pencil tablet can be useful. If investing time in it, using a display pencil tablet can improve workflow as well.

When drawing with the tools, we draw on the layers.

When animating, the entire layer will be modified between keyframes so it's important to use separate layers for separate objects.

The tools have the same properties as the sculpt mode with F for Size/Stroke, SHIFT + F for Strength and SHIFT + LEFT CLICK to smooth.

The drawn shapes can also be edited in Edit mode.

When erasing, you can use different selection modes with either Dissolve, Point or Stroke. The latter being most effective to remove an entire stroke.

Shapes can also be deleted manually by selecting them and using X.

The different layers can be found in the Dope Sheet for the animation of Keyframes and also in the Data panel.

The Trim tool can be handy to lasso select parts of the drawing that are sticking in/out and automatically trim them.

It's important to understand that each stroke is made using a certain Material.

The different materials can be modified in the Materials panel.

Materials can have either a Stroke , a Fill or both activated.

Using a Fill material (on a Fill layer) can be used to fill in closed shapes.

Usually one click works (since Blender 4.5) but if not, this can be modified with the Fill brush selected under the Tools panel > Brush Settings > Advanced > untick Visual Aids (which requires two clicks to fill instead of one).

Contrarily to 3D animations, Blender will not interpolate movement between keyframes.

Every keyframe for a layer will modify the entire content of the layer, this is why separate objects should be in separate layers. Especially when animating.

If Auto-keying is enabled (and it should) drawing on a new frame will automatically grey-out the content from the previous keyframe in green. If content for that layer is keyframed at a future keyframe, that keyframe will also displayed in a greyed-out purple.

This is called Onion skinning and can be toggled on/off next to the layer name.