Grease pencil workflow for composition or storyboarding Note to the readers, August 2019: Grease Pencil has gone through a major redesign for version 2.80, so you should probably check more recent resources than the (current) answers to this question




I would like to use the grease pencil for 


sketching the composition of illustrations
sketching the storyboard for animations


where the illustration/animation will be done in 3D.

For the illustrations, I'd basically like to "place" the different objects of my scene in the 3D world, and I would like to know the best way of doing this. For instance, for making the setup below, I had to go back and forth from mouse to keyboard to graphic tablet in order to move the 3D cursor (to choose the depth at which the line would be drawn), go back in "draw" mode, and do the actual drawing; to replace a wrong stroke I had to hit "Undo" because I'm not sure how to reposition a stroke.



Is there a window layout and a set of hotkeys that would help me?

For the animations I'd like to do just the same, but also to be able to make elements appear/disappear, and possibly to keyframe their Rot, Loc, Scale. 

Maybe this is all very simple, but I don't quite get the mindset behind all this: Are strokes objects? Where are they in the outliner? Do they have F-curves? Is their visibility keyframable? Does it change anything if I draw a stroke while being at frame #n rather than at frame #m (unlike regular objects)?



Wrapping it all up: I can't seem to find many tutorials, and the few I've found seem to focus on making 2D animations with the grease pencil itself. I'd really appreciate if you could introduce me to the right mindset that I need to work with G.P. as a "sketching" tool, and possibly some good resources about it.
To draw with the grease pencil at a specific depth and angle it's often easiest to simply place an mesh in the scene and orient it so the surface is positioned where you require the GP lines and use the Surface stroke placement to effectively draw on that surface. You can then either hide the mesh (to use it later to re-draw something in the same place) or move it to another location to draw the next stroke.



For animation of grease pencil strokes there are a couple of options.

The first is to convert the grease pencil strokes into 'real' geometry using the Convert... tool in the tool shelf.



This will create a curve from your grease pencil strokes and this can be manipulated as for any geometry.

The other (pure grease pencil) option is to use the grease pencil Enable Editing mode and the Grease Pencil tools in the properties side panel of the 3D view.



Firstly, use the Grease Pencil layers to keep your different elements separate. This allows easy manipulation of the different layers. For example, to select all of one particular layer (when in Edit mode) you can simply hide all other (by clicking the eye icon in the Grease Pencil layers list) and the press A in the 3D View to select 'All'. The layers can be assigned individual colours in the Grease Pencil properties panel if desired. 



To manipulate particular GP strokes, enable editing by clicking the Enable Editing button in the Tool Shelf (T). You can now use the usual selection tools (A for 'all', Box Select (B), Circle Select (C), etc.). Once you have selected the relevant points on the strokes you can use the usual Grab G, Rotate R, Scale S tools as well as Proportional Editing, etc. to manipulate the strokes.

To keyframe the changes simply swap to a different keyframe before manipulating the GP strokes. This will automatically create a new keyframe for the new strokes' position.



Additionally, enable Onion Skinning to allow you to see how the grease pencil strokes vary between adjacent frames.