Does anyone have advice for shooting with iron sights?

Spend as many rounds as they will let you: zeroing. Even if you think you are good, shoot more. If allowable, put whiteout on front sight post.

funny, I have the exact opposite problem, can't shoot worth a darn with a 68, god's gift to marksmanship with irons. My advice is blink, your eye goes through a lot more stress with irons.

It's all about Brass
Breathe
Relax
Aim
Stop
Squeeze
I am an Iron Sight Marine, currently I rotate between my BUIS and my optics. In a short range environment my Fixed sights are comfortable to me. I imagine the ACOG is your go to sight. As I transition from optics to iron I average about 500 rounds a month.
Create a regime, Running to contact, Barrier shooting, fixed position. Use both types of sights so the transition becomes normal.

Maintain a proper sight picture, breath control and trigger squeeze.

I learned to shoot a rifle with iron sites and a pistol with iron sites when I was 14. All the basics others mentioned were key to shooting squirrel sized targets at distance. When I applied my skills to an M16A1 at 20, sight picture, breathing and trigger squeeze helped me qualify Expert. I stayed with iron sights until age 40, when fielded with optics. I actually found them cumbersome at first, but learned to over-rely on them. So, bottom line, practice the basics and shoot as many rounds as you can. Good marksmanship is very perishable. By 49 I could still qualify expert with a pistol, but my rifle skills degraded to sharp shooter. Just too hard for me to see all the far targets anymore

I only ever shot with iron sights for qualification and fired expert 3 times in a row. It is all about the fundamentals. Sight picture, steady breathing, you have to really work on "snapping in" and get comfortable in your shooting positions.

You also need good dope on your rifle. There is no substitute for that either. Lots of little things add up to being in the black.

SSgt Dan Montague . My son is still in the Marines. They still use iron sights on known distance (table 1) firing (200, 3000 and 500 yards). They use optics on table 2 firing as I understand it.

When I was teaching markmanship, some of the things that were problems were: proper sight picture, proper trigger control on respiratory pause, concentrating on the front sight rather than the target. You should be able to look at your target and see which fundamentals you are missing. Good advice from previous posts.

Good cheek weld, even mark with tape, concentrate on the front sight (most common mistake) trigger control, front sight centered.

PMI PMI PMI. Can't say that enough. Break out the book, get back to basics. Washer/dime drills. Breathing excersises (look for your natural pause). Good cheek weld. Trigger squeeze.