I'm a bit late here, but my recommendation is to learn basic Java first and get the hang of how it works and how to debug. Then start by learning Java2D, although you can do without it I recommend it to get a feel for basic UI and OOP programming. Once you're good with that then learn other APIs like Libgdx. To learn Libgdx, you should learn how OpenGL basically works, don't go too deep though. Then watch Dustin Riley's tutorials and maybe get into GLSL later. It's a long process but it will help big time. I can't say I'm a Java expert (heck I still prefer null layouts
) but I think this should get you fluently programming in Libgdx. Don't forget to refer to the wiki and also refer to https://github.com/mattdesl/lwjgl-basics/wiki
(all of it, not just the Libgdx section). As I said, I'm no expert so feel free to correct me in anything I say.
Hope this helps.