Almost step by step:
Constructing a Basement Home Theater
You may need to pull a permit from your city or town to do this project. In some cases you must, and you probably want to anyway, put electric outlets no more than 12 feet apart all around the room with an outlet within 6 feet of every doorway without stretching cords across the doorway. (This is what the code specifies and almost guarantees that your subwoofer will have power wherever you put it.)
Don't forget that the speaker wires inside the wall need to be rated for in-wall installation. Romex type cable works equally well for speakers as does speaker wire.
One thing I put in that is quite unusual is an electrical circuit serving a few selected areas of the room including for a ceiling projector location and which terminates in a "male receptacle" in the wall instead of at the electrical panel. This is to accommodate a battery backup unit that in turn plugs into the nearest (regular) receptacle.
I know that my setup is very lacking in sound insulation. Namely I do not have double studding with insulating batts weaving back and forth inside to protect other parts of the basement; the heating ducts are shared with the rest of the house and let the theater sound go to all corners of the house; and the basement ceiling has only the original insulation and sound comes up into the kitchen above.
A floor covering is almost a must to keep the heating bill down in winter. I am trying to decided between just a (reasonably thick) carpet versus a built up floor using such materials as Dricore. But too many layers of carpet and padding could result in moisture buildup followed by mold on the concrete floor when that is cooler than the room temperature. This would vary from one house to another.
I chose to not relocate any pipes or ducts, working around them and leaving some exposed whichever was easiest to do.
Dehumidifying in summer will probably be needed.