You seem to be doing quite fine. Can you be a bit more specific what you're struggling with?
The boat and horse look lovely, but without knowing what your goal was, it's hard to say what you should do to improve (anything I would say would go towards a specific art style of my choice, but is not my idea to influence your direction). Isometric piece looks good too, although I'm not sure if you literally copied one of their pieces or just did something on your own in their style.
So in general:
1. know what you want to draw
2. try and draw it
3. see where the end result deviates from what you wanted to draw
4. find internet resource for those specific problems
5. apply the new knowledge on your next work
That's my approach to improving anyway. Sometimes there's also step 1.5 (similar to #4) where I look for tutorials in advance if I'm not sure about the process.