Tutorials/tips for Normal Maps?

Hello folks,

I’m interested in using Aseprite to create normal maps for pixel art so I can add some depth to my pixel art, but it’s quite tricky. I’m following a this game for GameMaker: Using Normal Maps to Light Your 2D Game
So I was wondering if anyone has any tips or good tutorials for drawing out normal maps in Aseprite. A quick google search didn’t really reveal much.

Thanks.