I once owned an Ithaca Flues model 2-E 20-bore with 26" barrels; it was a beautiful light weight little gun but I couldn't shoot the thing worth a dang, it was just too light. Had the same issue with a 28-bore VH Grade 00 framed Parker; it was just too light, and with both guns I became a "poke and shoot" gunner. These guns were so light I found myself just reacting and failing to remember basic shooting fundamentals. But that was 20 years ago, might appreciate that light weight now as 12-bores feel much heavier at age 70 than they did at 50.
About ten years ago I found myself having to learn to shoot ultralight .410s, to prove to my 8 year old grandson that a .410 was an effective dove gun, not just an "appeaser" for kids. What I found was that I developed an entirely different shooting style than with any of my other guns, which were a minimum of 2 lbs. heavier. I learned to mount the gun as I was swinging on the dove, and when it hit my shoulder pocket the lead was almost already right, and hit the trigger. Really more of a fluid move than I was used to on my heavier guns. The little thing only weighs 4 lbs. 14 oz., but I was able to soon get the hang of it and now even shoot some of my 28, 20 and 16 ga. dove guns with that method. It's highly effective for me with lighter guns.