I have an old supro dove copy, I'm guessing from the mid-late 60's. not a nice guitar by most standards, but I'm looking to see how I can improve it. I know very little about customizing acoustic guitars but have done some work on electrics. here's some things I could use advice on:

1)the action beyond like the fifth fret is ridiculously high, i cannot physically play barre chords. is there a way i can fix this? truss rod adjustment? sanding down the bridge (how do i do this)? not sure if it can be done but let me know your thoughts.

2)improve the sound. I've heard a new nut can really change the output of a guitar, not sure how much truth there is to this, thoughts? also changing the saddles maybe?

I'm determined to improve this guitar and could really use the help of the internets, so many, many thanks in advance.
The action is dependant on numerous factors. It's really simple geometry, and it goes like this: If the string is to far above the fret, make it closer. If it's to close, make it farthur. Sounds simple until you consider a neck that's not perfectly flat, one that may be wavy, and the difficulty of actually adjusting these things (sometimes, some guitars are very easy, others, not).

As for your supro, check the neck relief. I won't explain this as many others already have, google it. If it's wrong, make it right.

Neck relief being good, check the saddle height, could be to high, if it is, fix it. Again, google it.

Nut could be to high, if it is, fix it, google it.

But there are other factors too, the neck might not have a perfect relief to it, it might be wavy or the frets uneven. In this case, it's a little more difficult than a twist of a truss rod (if your supro even has one) or sanding down a saddle.

As for tone and nuts, that will only make a difference on open strings. Think about it for about two seconds and it makes sense. Anyone who tells you otherwise is obviously more versed in voodoo than I. Good luck, old guitars are fun.
Last edited by LeviMan_2001 at Mar 8, 2012,
On a guitar that age there's also a possibility that the soundboard has "bellied out" as the bridge gets rotated toward the neck as a result of the tension on the strings. If that has happened it won't be helping the action (or the sound, probably) either.
Basically what LeviMan said.

1. Check neck relief with an accurate straight edge.
2. Adjust bridge height if needed by sanding down the saddle/adjusting string slots.
3. Adjust nut height if needed using feeler gauges, sanding the bottom of the nut, and adjusting string slots.

Also bear in mind that frets could be worn down and it might need a fret levelling/crowning.