I've done tons of tilesets both with photoshop and as pixel art. However I'd like to learn more about them from a design standpoint, and just improve myself in general. (in addition to just practicing) So, are there any education resources online that cover tilesets in-depth, particularity for platformers?

Just to clarify, I don't mean a pixel art tutorial or just how to make tilesets.

I'm not sure that I fully understand what you are asking, but here is a short article that I thought was interesting (mostly the part about metroid). Not sure if it is what you are looking for though. What kind of tilesets do you make? What type of games do you make them for? I'm just curious because I also enjoy creating tilesets and it's a topic I'm interested in.

I'd just like tips on making tilesets, basically. As for what kind of tilesets I do, tilesets for 2d platformers mostly. (think snes games like castlevania, megaman X, etc.)