Lot's of good advice given here. There's nothing much I can add other than to confirm the most important things that others have said...
-Have someone else coach you for a few practice sessions It doesn't take an expensive class to learn marksmanship (it helps, but you don't have to have it). An RO, a trusted buddy who shoots and shoots well (and is somewhat intelligent), or the guy you shoot next to that knocks out the 10 ring at 10 yards every time with a pistol.
-Trigger control... you get that by dry-firing and practicing. Trigger control is the ability to pull, squeeze, press (whatever you want to call it) the trigger without moving the gun as a whole (or flinching, which definitely moves the gun as a whole). Dry fire is a good and free way to practice this. It is such an effective tool that the United States Marine Corps, known world-wide producing competent marksmen, forces it's recruits to spend a whole week dry firing before anyone ever fires their first live round. You can have a poor grip and still produce acceptable groups if you practice proper trigger control. Another good technique when you're beginning is to have a friend load dummy rounds and live rounds in a magazine and watch you as you shoot. If you have a flinching problem, the friend will see it when you pull the trigger on a dummy round
-Focus on the front sight post. It should be clear and the target should be blurry. This is the one thing that I learned when I was in the Marine Corps that took my abilities to the next level. I was a good shot before, but I could not make a 500 yard shot with iron sights for nothing. Learning this gave me that ability.
As others have also said, 10 rounds of quality practice is better than 100 rounds of junk practice. I grew up shooting rifles, and was darn good with one before I joined the Marine Corps. Never shot a pistol before then. To my dismay, when I went to coaches course I had a hard time with the pistol due to inexperience. After a couple of days and a few hundred rounds, though, it "clicked" and I got it. It was trigger control the whole time for me. I further refined my groups by proper grip, stance, "push pull," etc. Once it "clicks" for you though, it's all downhill.