As far as people getting nice shapes and structure with very few brush strokes, that's mainly experience there. As you see things more an more clearly in your head, it'll make it easier to put things on the canvas. Another tip would be to start with a big brush first and then work your way down to the details.
Now if you struggle with getting the right values when starting in color, do value paintings first. I recommend doing a line art first. that way your only focusing on your composition and story. Values come second to help reinforce the composition and storytelling but it's the lighting step. You make sure things are lighting up alright before the final pass with colors. When going into the color stage there are a few ways you can approach it. One way is to use gradient maps. If you feel you need more color then you can use adjustment layers.
So long story short break things into simple steps so your not tackling to much at one time like you are with jumping into colors. In time you'll get there, but, in the beginning keep things simple.
As far as this piece goes, it seems really saturated. I'm not exactly sure what the story is here. Is it someone just looking at a sun set? Because of the colors and brush strokes, I wasn't sure if what the character is under is a space ship or some rock structure. Something that needs to be defined for the viewer. The image also feels flat because the depth in the image isn't there. The sun feels really really close to the point I think the character would die. Maybe that's what you were going for. I don't know.
Other things I think are important to mention is that feel you should practice perspective. Understanding this fundamental would vastly help you. Other than that, you can actually go back and watch Marc's tutorials on shading. Here's one on improving color shading. It's old but still great.
Now this is not a failure. I know I recommend a lot of things and hopefully didn't come off as ruthless because that can be counter productive. One important thing you did was keep me in the piece. You had points of interest which is great.
Welcome to 
Happy to have you here. I'm sorry if my post was to long. Keep up the good work. I look forward to seeing how you improve.
