I've been doing this free class on Coursera (sign up and click enroll button): https://www.coursera.org/learn/pixel-art-video-games/
It teaches some pixel art (also some general art) and how to get things into Unity. It's not too good in my opinion, but there's a few decent tips in there, so maybe it will help. It assumes you're using Photoshop for pixel art and Unity for the game engine.
Also, here's some pixel art links to check out:
- https://pixelation.org/
- http://pixeljoint.com/
- https://lospec.com/
- https://lospec.com/pixel-art-software-list
- https://lospec.com/pixel-art-communities
- http://purloux.com/artwork/tutorials/
- https://androidarts.com/pixtut/pixelart.htm
- http://makegames.tumblr.com/post/42648699708/pixel-art-tutorial
- http://pixeljoint.com/forum/forum_posts.asp?TID=11299&PID=139318#139318
- http://blog.studiominiboss.com/pixelart
- https://medium.com/pixel-grimoire/how-to-start-making-pixel-art-2d1e31a5ceab
- https://medium.com/pixel-grimoire
- https://www.youtube.com/user/atMNRArt/playlists