I'll be picking up my new (and first) shotgun this week and while I'm expecting a first-quality product ... I have also been reading some horror stories of problems straight out of the box. It's an 870 Express Tactical, specifically an 18 inch barrel, one-piece, six-round mag tube, "Plain Jane" entry level HD ordered from Bass Pro.
To be honest here, anything too technical will be lost on me; so in the simplest terms:
What should I look/listen for upon initial inspection?
How should I prep it for the first trip to the range?
What are some common problems (and solutions) I might encounter putting the first 50-100 rounds through it?
In the likely event I missed a key question please feel free to jump in with the answer

FWIW, my experience is with handguns; Smith & Glock, very different animals from a long gun ... a pump action at that.
Thank you kindly,
Matt