I've been hunting for a number of years and I still miss (ahem, twice this weekend - the dog hates me for it!). Don't wear ear plugs, you can listen for the birds rustling on the forest floor in leaves, hear where they flush and sometimes hear them settle in the trees.
If you know your property well enough, and flush a bird but don't get a shot off at it, don't be afraid to mark where it flew and go after it. I learned today that the buggers in our bush lot fly far, much farther than I expected, sometimes land on the ground again, and sometimes not, and that they bird that gets flushed 5 times deserves to live!!! LOL.
As far as the safety on the gun goes, it is on until I am ready to shoot and when I have a presentable safe shot then I take it off for my shot, after the bird is shot before I move my feet again, it goes back on. Is a stupid grouse really worth you or someone else getting injured? To me, if you don't get your safety off fast enough for a shot because of a sneaky grouse popping up then you need to go back to hunter safety course 101. It's simply not worth it. Keep it on until you can shoot safely.