I'm no expert in this, but I think step 1 would be deciding between vectors or pixels. For this it would be important what the use-case is. Vectors are cooler,

I'm no expert in this, but I think step 1 would be deciding between vectors or pixels. For this it would be important what the use-case is. Vectors are cooler, but you'll need more magic for performance I bet. With that decision done maybe just throw together a small iterative prototype to try things?: draw a straight line, draw it with the cursor/mouse/touch, draw a spline, draw free-hand. Layers, saving, blending, brushes....