I'm not the best example to learn from. But if you want to get in the room, I can show you the door. :)
Phh the digital drawing is just a tool, you can apply the same skills and knowledge that you have for drawing on paper or canvas to it. The key to it is to study the fundamentals. How a silhouette, shape, light, and values work. After that, you need to learn color theory and then, composition.
For start i can show you this. This is a tutorial playlist by one of the best in the craft. Scroll down to the first video and start from there, after that you can look for Anthony Jones. That dude is godlike! But yeah. Grind the fundamentals, anatomy. The rendering is just patience. The sketch is where everything starts. If you set it up right, everything will be alright. If you screw it up it up, in the process the mistakes will start to pop up and it's harder to fix a half- done painting than a sketch.