Spriting Advice

Hey there folks. I was wondering, since this is a place where game developers of all kinds gather, what resources did you use to learn how to sprite? I find I've been doing a lot of solo work, and my graphics skills leave a lot to be desired.

I'm currently using Aseprite as my editor of choice, but its inability to work on tilemap sprite-sets without just working on one large sprite is making it difficult to do some of the things I'd like to do.

You can see probably the best spriting work I've done yet in my LD40 game, Factory Panic. The ore was done with a Wacom tablet and Aseprite's gradient tool. The player character's sprite is very roughly inspired by the player sprite from Journey to Silius.

Any help would be appreciated, and thank you for your time!