Improvement is hardly seen over a few days, hell, over a few weeks.
You just must keep drawing and then, after about a year, look back on your work and judge it. Being able to judge is and criticize it properly, to me, is improvement. If you can say: "Oh, I drew those eyes too big, or that hair is off, or her legs don't look right there," then you've improved enough to see what you've been doing wrong and therefore you've fixed those particular problems.
I don't know if that makes sense, but that's how I see improvements XD