Been there, done like that. Doves have been my reality check. Every time I get to thinking I'm Hot Stuff with a shotgun, dove season reminds me there's still a ways to go.
I have gotten better over the last half century. Haven't been out yet this season, but last year I used the little SKB 20 and 7/8 oz loads to good effect.
IIRC, 9 birds in 17 shots. Of course, I've returned plenty of lead to the earth getting to this point,including 500 or so through that SKB just prior to the season. That's a hint....
Here's a couple things that may help boost your average....
Know what 40 yards really looks like. Pace it off when you set up and limit your shots to within that. I've used decoys as range markers for the longest time.
Pattern your shotgun with the load and choke you'll be using. Check for POI and spread. While us writers like to talk about 30" of spread, 26-28" of good distribution is much more common. POI should relate well with POA, a little high is OK.
I prefer 7 1/2s to 8s, but the difference may just be in my head. More important than shot size is shot quality. Hard round shot is the way to go.
I used to use trap loads, but now I load target quality reloads that pattern tightly and keep all the pellets effective. 7/8 oz works for me.
And know your gun. Shoot just that one and do so frequently.