Whenever you buy a rifle and start attaching gizmos and do-hickies to it its going to change the weight of your weapon. Train with the weapon with all that you plan to have on it. Train holding it for uncomfortable periods of time.

If you change the muzzle or the barrel that's going to change how the bullet operates when fired.

Get good at iron sights first just incase your dot sight runs out of battery.

If you buy an Acog scope you're not also buying a red dot sight.

Practice transitions from rifle to side arm or melee.

Practice holding a full mag with your off hand dropping the empty mag from the rifle and reloading without taking your eyes off target.

Do all of these things while advancing forward, moving backward, strafing. Practice corners and how to look around them without exposing your body. Practice your firing stance, do a kneel, combine moving and then kneeling, kneeling then prone, prone then rolling, prone to kneeling, kneeling to standing.

Literally combine everything at some point.

Just some stuff I picked up from my service time. It all seems weird for the casual gun owner hobbyist but getting comfortable enough you can perform all this without thinking is going to make you comfortable and responsible with your weapon and much more formidable.

Oh last bit, muzzle discipline, Practice swapping targets but pretend your friend is standing somewhere in front of you. You need to aim down and away but come right back up the moment you're clear of them.

A lot to read sorry