I have a few tips from what I have learnt:
Small advantages matter. Things like the above mentioned running an SMG up close so you don't need to ADS is good.
Additionally, if you know enemies are close by, stop sprinting. Having your gun drawn an ready gives you an advantage over folks who need to come out of sprint.
SMGs, Carbines and ARs work for aggression, but LMGs generally demand a defensive approach. They're slow to act with, so try and get in positions where the enemy comes to you, ideally where you're in a crouched or prone position.
Intel is everything, so check your minimap often. If you know a guy is coming around the corner before he knows you're there, he's easy pickings.
Try to limit your exposed angles. If you've got hard cover everywhere behind you, then you only need to watch the front.
If you can handle the extra cognitive load, swap out the red laser module for greens and blues. The extra hipfire accuracy WILL save you in a sudden close quarters fight, just remember to turn it off when firing at range.
Hope this helps!
