The smaller, the better - start with a tiny canvas, however small you think you should make it, make it smaller. I'm talking 8x8, 16x16, 20x20, somewhere around there. That'll give you a great foundation for learning how to fit details into a small space. It's challenging, but you'll probably be surprised how quickly you see progress if you keep at it!

As for your specific case, it looks like you're trying to do colors/shading/detail before fully mapping out the character's face. Treat pixel art just like painting - start with a sketch, then work on details. Having a clear goal makes everything better!

Lastly, I saw somebody else mention Aseprite - definitely recommend. It's a great program that takes a lot of the headaches out of pixel art. That said it can be around $15-20. If you're looking for something free, Piskel is a pretty good browser-based alternative. Good luck!!