There are different philosophies on whether to "pre mount" a shotgun / or to shoot a "low gun" and mount as the bird is in flight .....
In general ( international games are different ) ...but in general, "pre- mounting a gun" is ok within the rules of Skeet, Trap and Sporting Clays.
Most of the time, I "pre-mount" the gun to my shoulder and my face - then move my eyes only, to where I expect to see the bird clearly, and call for the bird - or I focus on my hold point in Trap (beyond the house) since I don't know the flight path of the target. But in Skeet and Sporting Clays - you always know the flight path of the bird, where its coming from and you should have a "plan" on where to break it. In Sporting Clays, its probably more common to see shooters, shoot "low gun".
To some extent, the dimensions on the stock - may dictate what style stock, weight of gun, etc you choose to use. I've been shooting long enough, and had enough good advice, that I've figured those dimensions out - but most of the time, if a gun is labeled as a "sporting gun" for me, it has too much drop at comb and heel ... but it may fit you great. So it depends....
You're going to hit some plateaus in your Trap shooting. 15 to 18 is a good start ( with a goal of not missing more than 2 birds per station ) / as you transition to 19 - 21 then reset your goals, no misses of more than 1 bird per station. As you go to 22 - 23 average / you need to go straight on some stations - and expect it ! To average a 24 / means 96 out of 100 obviously - so you need to run some 25's / with the goal of never shooting a 23 ( no matter how windy, etc it is that day ). When you shoot a 23 ( with your goal of a 24 avg ) you need to bear down ... and get it back with a 25 on the next squad out.... Don't be hard on yourself / be realistic -- work on hold points, foot position, staying relaxed, calm, one shot at a time, find it, feel the lead, kill it and follow thru ( no quick or uncontrolled movements ). Quick is ok / if its controlled ... Be aggressive / but don't "slap" at a target... Head is always on the comb / eyes are always on the Target and nothing else / and follow thru and keep the gun moving on the target path as the target breaks .... ( my average at the 16 yd line is around 23 / not 24 ... / but an occasional 100 straight still feels pretty good.