I've read a lot of stuff on this subject and measured my own guitars.
Some of the tests I've read even my new guitar that plays perfectly
didn't pass so I've come up with some sensible things to look at. This
is for steel string flat top acoustic guitars only.
The first and most important thing to consider is, if you think your guitar plays great, there probably isn't a problem. If you're hearing extreme buzzing or your guitar is too hard to play, check out a few things.
First, sight down the neck from the tuner end. You shouldn't see any twisting or bumps especially where the neck begins to go over the guitar body. The neck probably won't look perfectly flat. This is normal. The neck will probably have a slight concaveness around the 6th fret. We'll check more on that later. Now lay the guitar someplace good like in it's case and measure a few things. Get a good metal straight edge that has measurement lines to the end. Stand the end of the straight edge on the face of the guitar in front of the bridge. You should measure about 1/2 inch from the face of the guitar to the center of the Bass E string. My guitars measure a hair more, but I'm a heavy player and like my action higher. Now go to the 12th fret on the neck of the guitar. Stand the end of the straight edge on the TOP of the 12th fret. There should be about 1/8 inch from the top of the 12th fret to the BOTTOM of the Bass E string. Again my guitars are a hair higher, but that's my personal preference.
The last thing to check is that concaveness in the neck's fretboard mentioned earlier. With your left index finger, push down on the Bass E string on the first fret like you're playing a F. With your right index finger, push down on the Bass E string at the 12th fret like you're playing a high E. Now look between the bottom of the Bass E string and the top of the 6th fret. You should be able to see a very slight gap. Just enough to see some light.
Above are just general things. Some players like things set up higher or lower. The thing to remember is if your steel string acoustic guitar doesn't play right to you and you see anything that departs greatly from what's mentioned above, you probably need a qualified repairman to check things out.
Bob, Gman ( o )==#