Well, when starting to learn pixel art for the purposes of game-making, you need to consider what you're trying to accomplish and how you're going to use the stuff you make. Before learning isometric pixel art, I'd suggest figuring out if you can make an isometric game first. I believe Game Maker supports isometric tiles, but Game Maker is annoying to work with.
That said, I don't really recommend isometric pixel art in that style because it's a bit of a dead end. I see that style everywhere, and it's all exactly the same. I mean yes, anything can look nice, but I see a lot of isometric pixel artists fall into a rut. Tackling something a bit more complex would probably help you grow as an artist more--but not too complex to start with.
Pixel Joint has a lot of fantastic artists you should study for inspiration. Check out the weekly showcase and the monthly top 10s.
The sprite itself looks decent, but it's so simple there's not really much to comment on. The line separating his arm from his chest goes up too high, and his hands could use more definition, and you could shade the far parts of his body more.
Basically what you should be trying to learn right now is how to make beautiful pixel clusters. Pixel art is basically about pixel clusters, groups of pixels arranged in aesthetically pleasing ways. You want to focus on that and not overcomplicate it with lots of detail at this point, but you need to tackle something that actually makes you think about depth and light sources and whatnot, which sprites in that style don't.