First of all, it takes literally thousands of rounds of practice to develop into a good pistol shot. So the main way to improve your shooting skills is practice, practice, practice.
But you have to practice the right techniques. The members who suggested having a shooting instructor evaluate your skill had a good idea.
I am not a Glock fan -- good gun, just not for me -- but at that range the Glock should be reasonably accurate, even with it's long trigger pull.
In brief: make sure you have a good, steady hold on the gun; a well balanced stance; a slow steady pull on the trigger -- squeeze, don't jerk; breath control (breath in, let air halfway out, hold beath during final squeeze of trigger; and make sure you aren't flinching or jerking in anticipation of the gun going off. Don't try for speed at first, try for accuracy. Make sure you are getting a good sight picture; line up front and back sights, focus on front sight, not target.
Look for more experienced and good shooters at your range, ask them to watch you and see if they have any advice.
Edit: It is very important when first learning to shoot that you be AWARE of everything that you are doing. Before you start to shoot, check your balance, make sure your stance is steady. Have you learned the basic stances -- I use a modified isosceles, some like a weaver oriented stance. If you don't know what these are, you need to learn and try them. But FEEL your balance before you shoot. THINK about your sight picture. CONCENTRATE on a slow even squeeze. Eventually these acts will become second nature, but at first you need to consciously take yourself through the steps.