As a general point, you need to work on anatomy band proportion right now. That will tremendously help your line-art. Still, you also need to keep practicing shading and some high-end pieces every now and then instead of constant sketches. It helps you to grow and serves as a better benchmark for you being able to track your own growth. You also need to work on rounding out your figures a bit, because they seem flat. You're not thinking in 3D, just in 2D-- it's a hard step but you can get better with practice.
As far as your improvement rate: there's not right or wrong speeds. You'll definitely improve faster if you draw more often, but everyone has to get the basics down-pat before they're amazing. In the year you've been drawing, you've uploaded a total of 15 items. If that's the amount you've drawn, you aren't going fast enough to improve at a steady pace. At least draw once a week (even if you upload it or not) so you stay fresh, preferably draw every day. I spend at least 5~10 minutes sketching every day, and that's before I get into serious drawing. Get your feet wet often and you'll see an improvement like you want.
Like Zydala said, we're here to help you out-- ask for critiques redlines and someone around here will get around to it. You can even join my drawing class if you're having trouble or you're curious-- link's next to the red words in my signature, and everyone there will be glad to have you drop by.
