Being a complete novice, I took time to read this thread and learn, now I have, it's as clear as mud..
I have not bought my first gun yet, but I'm desperate not to make a wrong or rash decision.
Hey Harley. I'm new here, but no stranger to shotguns. I actualy shot target rifles competitively for quite some years, before I came back to clays.
In that time, I learned how important gun fit can be. At least with a rifle, you have two sights to align the gun with the target...but on a shotgun, your eye is the rear sight...so it has to be in the right place.
As you have not yet bought a gun, you are in a good position...but...don't worry too much about having something that fits out of the box.
I'm not sure what you intend to spend, but your main consideration should be to buy something that you like...ideally of reasonable quality...even if that means secondhand.
Find a reputeable gun shop, with someone who knows a bit about gunfit...
Assuming it has a wooden stock, most guns can be made to fit just fine.
Modern guns are generally made to fit a 5ft 9 male, of average build...so if that is you...you will do well.
For everyone else, some changes might be adviseable.
As you are new, your gun mount will take time to perfect...but if the gun were unloaded, and a person where to look, down the rib at your eye while it is mounted...the coloured part of your eye, at the bottom, should be sitting just on the top of the gun, with the pupil centered along the rib.
It could be that you aren't centered and are looking along one side of the gun, or your eye is too low behind the breech...which will cause you to lift your head...and so on.
An experienced shot, can learn to shoot an illfitting gun...and so to could you learn to shoot one, but you will have inconsistency and unexplained misses...which leads to frustration and perhaps even giving up alltogether...we can't have that!
Do a bingle search on gun fit, perhaps articles by Mike Yardley...they will help.
http://www.positiveshooting.com/GunFittingP1Main.html
I had to make mine fit!