A lot of good advice here. If you think or dont know if you are flinching try this. Mix some dummy round in with your reg ammo. (this works best if you have a friend do it and a few mags) When you pull the trigger on the dummy round you will no doubt know if you have a flinch. Focus on maintaining sight picture, trigger press and follow through on each round.
I do this frequently. my 2c

BLACKBRIAR just named the main things that improved my pistol accuracy exponentially. I was taught his "snap cap" trick when I first began shooting handguns and it helped A TON in eliminating my flinch as well.
TIPS:
1. Use the above trick. At the range have a friend load your mags, peppering in snap caps every few rounds. When you pull the trigger on a dummy round, you will probably flinch. Eliminating this flinch and thus properly maintaining your sight picture when the shot breaks is the most important factor in improving overall accuracy.
2. Find an accepted stance and grip that feel the most comfortable to you and stick with them.
3. Aim using your dominant eye, but leaving both eyes open if possible, and make sure your front site is in focus and the target and rear sight are slightly blurry.
4. All together now. Take your stance, steady your breathing, aim carefully holding on target, and squeeze the trigger straight back evenly so when the shot breaks it "surprises" you. With practice, this collective action will become automatic and natural, and once mastered can be applied to a variety of shooting scenarios.
5. Practice as much as you can afford to. Keep your mind clear and focused and build your muscle memory. (grip, stance, follow through, etc.) This will give you the confidence you need to shoot more consistently.
These ought to help you tighten your groups, especially if you can practice the "#4 ritual" while shooting slowfire at the range.
Happy Shooting