Everything we do requires a vast amount of time in order to notice improvements. Let it be soccer, basketball, softball whatever. There is this practice routine you continuously do to get better. And at certain stage you will become discourage, due of a slow pace of improvement. Do no falter, you're getting better. We tend this tendency of comparing our self with others work, and get discouraged...instead of getting discouraged see the one you're comparing too as an inspiration for you to get better.
One practical tool would be, check your current sketches/art and check one of your older sketches/art like way back. That can somehow, can motivate you and show you, you have gotten better. But of course, that's also a matter of how are you practicing. Are you doing it specific, or just riding along drawing whatever comes your way, and hoping to improve one way or the other.To show a demonstration of how I improved my gestures check out the image below:
I started this gesture challenge on 7/1/2014 and ended 7/31/2014. I wanted to reach 1000 gestures, but I didn't. Although I came close to it (900 gestures). What I want to show is, from the left is how I were drawing gestures , compare to the right is how I draw them now. Because I have learned a lot from my own mistakes and new techniques. And that's the beauty when you archive all your arts/sketches. It gives you somewhat a third person view of how you came to where you are now.
What I wanted to say is, art or any field requires mileage. It requires a tedious amount of repeating the same thing over and over till you get better. Don't give in, continue pushing. Eventually, all the tedious works will pay off.