drywall? plaster? Gotta watch for hidden things of course behind
   the wall. some of that's easy - electrical *usually* follows the
   studs up the wall (or down) - but in some homes, they do cut it
   across sideways - rarely diagnally! So look at each outlet,
   lightswitch, telephone box (for telephone wires). Then look at
   plumbing fixtures (sinks, etc) - same idea with them. heating
   fixtures, same ...thing. it all only takes a few seconds of
   glancing around the area. Then cut - carefully. I had a surprise
   a few years ago when I put a screw in drywall to hold up a
   shelf, to suddenly find water trickling then GUSHING out. Turns
   out, although my bedroom is FAR FAR away from bathrooms, etc -
   RIGHT ON THE OTHER SIDE of the wall was a hose bib ("spigot") -
   and the plastic ("pecs"/pex) was leaning against MY side of the
   inbetween-space. What a mess a pinho... "