Practice makes perfect is a saying that is everywhere. No matter what you wanna do, especially in game design. Do code, art, design, sound, anything requires a lot of practice. But finding the correct places to practice can be extremely difficult.
One place I have been loving to go for learning new art skills is Digital Tutors. They have a lot of great tutorials available for both 3d modeling and 2d drawing in things like Photoshop and Illustrator. I also use quite often Lynda Tutorials. Both of these sites are going to have a lot of tutorials to expand your knowledge.
Of course, besides learning more about the software and drawing styles, drawing in general is going to really help. One thing I have started doing is going on reddit.com . Specifically the subreddits called SketchDaily and DailySketch. Similar names and similar purposes, they post things every day that you can go ahead and draw, then you can post them and get critique on what you did! A lot of great feedback gets posted here, and it’s definitely a great community.
Those are just the art websites I’ve been looking into recently in order to start improving my art skills in order to match my coding. I’m hoping to continue evolving my art skills and start doing some rough digital concept art for the game I want to start working on!