don't lock your arms you'll just end up with sore elbows.
Here's the thing, start at 3 yds, yes 3 yds. Shoot at a 2 inch circle, focus on your front sight the entire time, and by focus I mean it has to be 100% the only thing you are looking at, the target and rear sight should both be blurry. Once you can all your shots in the 2 inch circle at what you consider a reasonable pace, step back 1 yd and repeat. Do this until you can do it at all the distances you want to shoot at. Once you're able to do that, then work on speed. Start back at 3yds and hammer the target as fast as you can, any shots outside the circle mean you need to slow down. Once you're successful move back 1yd. Repeat.
Most people think the above is below them, and every week I see a ton of new shooters that can't keep their shots in a 2 inch circle at even 1yd from the target.
Don't forget to breathe, don't stage the trigger, just pull it, smoothly and slowly, without disturbing your sights. It's that simple. The rest is bull####.