Yes. Which game engine? (it's best to put the software in your title, here's why) We have a lot of tips here. http://wiki.polycount.com/wiki/Landscape And here too http://wiki.polycount.com/wiki/MultiTexture
Some good overall 2D art resources here... composition, color theory, etc. http://wiki.polycount.com/wiki/Concept_Fundamentals The first link here is full of great advice and examples http://wiki.polycount.com/wiki/PixelArt
Yep. Especially in the games industry, where there are so many applicants wanting to get in. We have some great info here http://wiki.polycount.com/wiki/Game_Industry Also see http://wiki.polycount.com/wiki/Portfolio