scoring a song to guitar

I'm doing a little guessing here - "score" usually means put into standard notation, or to create an arrangement/orchestration. But I'd interpret "guitar progression" as a chord progression arranged for the guitar. So I'm guessing what you want to do is create a chord melody, which is taking an existing arrangement and working out a playable guitar arrangement. If my guess is wrong, let me know and I'll try again :)

Since it's the Christmas season, I'll illustrate this by working out a chord melody for the beginning of "Silent Night".

You'll want to start with both the melody and chords to the song you're going to do. The beginning of "Silent Night" would look like this for melody:

-----------------
-----------------
-0-2-0---0-2-0---
-------2-------2-
-----------------
-----------------


That part is played over a C major chord. Like almost all songs, the chord were chosen so that most of the melody notes (six of the eight notes so far) are chord tones. Only the two A notes aren't part of a C chord.

Our ears tend to hear the highest note in a chord as the melody in most cases. Sometimes we'll pick up on a melody in the bass line. But we rarely hear voices in the middle as distinct melodies. So the first thing we want to do is move the melody up an octave, so it will end up being the highest note in the chords. Here's one way to do it:

-3-5-3-0-3-5-3-0
-----------------
-----------------
-----------------
-----------------
-----------------


Now we want to construct C major chords on those notes. Since the A note isn't part of a C chord, you have two choices: either play that as a single note, or alter the chord so it contains the melody note. I'll take the second path, using a C6 chord (which is identical to Am7):

-3-5-3-0-3-5-3-0-
-5-5-5-5-5-5-5-5-
-5-5-5-5-5-5-5-5-
-5-5-5-5-5-5-5-5-
-----------------
-----------------


The fourth and last chords could have been played x32010 as an open C chord, since that also has the open E string as the highest sound. But you can make choices on the guitar, and here I've chosen to stay in one position, doubling that high E on the 2nd string.

The next part of the melody is played over a G7 chord, and goes like this:

-------
-3-3-0-
-------
-------
-------
-------


A G7 chord contains the notes G, B, D, and F. So we start with the highest note, D - moving it up an octave puts it on the 1st string, 10th fret.

With the D figured out, we still need G, B and F. You want the chord to be playable, so it's a good idea to start writing arrangements like this by working your way across the strings. With that 10th fret D, you could put F on the 2nd string (13th fret), or you could put G on the 2nd string (8th fret).

If I put F on the 2nd string, I've got this: x-x-x-x-13-10. I still need B and G. The G is at the 12th fret, which gives me x-x-x-12-13-10. One voice left, F, which I have to put on the 4th string - that's at the 15th fret, and I get this: x-x-15-12-13-10.

Since that doesn't seem like the friendliest chord in the world, even though it's playable, I'll try using the G on the 2nd string, starting with x-x-x-x-8-10; I still need B and F.

There's a B on the 3rd string at the 4th fret, which is out of reach, and an F at the 10th fret. If I play x-x-x-10-8-10, I still need B, which is 9th fret 4th string, and this one looks playable: x-x-9-10-8-10. I'll do the same process with the next note in the melody, and I get this:

-10-10-7
--8--8-6
-10-10-7
--9--9-5
---------
---------


You basically keep following that process until you're done.

When I teach chord melody construction, I prepare students by giving them a "tool kit". There are about 100 ways to voice any given chord on the guitar, which can make it seem overwhelming. But since the melody is constructed on the soprano (the highest note in the chord), you can really start with just one chord form for each chord tone. Silent Night is made up of just major and 7th chords in the harmony, so you'd need seven forms:

C Major: xx10-9-8-8 (to put C in the soprano), xx2010 or xx14-12-13-12 (to put E in the soprano) or xx5553 (to put G in the soprano). I encourage four-voice chords for the most part, as they're easier to work with, but give you a full sound. You can extend them to 5 or 6 strings if you'd like.

G7: xx3433 (G soprano), xx5767 (B soprano), xx9-10-8-10 (D soprano) and xx0001 or xx12-12-12-13 (F soprano).

Using those voices aren't the only option, but they'll give you a playable arrangement... which you then use as a starting point to figure out better fingerings - as I did for the xx5550 C chord in the beginning.

I hope that's what you were asking for :)

I forgot to mention... for the F chord later on in the song, you simply transpose the C chord voicings, getting xx3211 (F), xx7565 (A) and xx10-10-10-8 (C)

And, if what NoteBoat posted is the sort of thing you are thinking about, there's a bunch more lessons on chord melody here