Look at the structure of the guitar music. Find what key the song is in by looking at the first and last chords. If the song remains in the same key, both chords will be the same and that chord will be the key the song is in. It is important to find the point at which a song changes keys if that is the case. Look for an alteration of chord patterns, then find where the new pattern begins and ends.
Determine how many sharps and flats are in the key signature. Note any minor chords within the song.
Find the meter of the song. Meter is indicative of the rhythm to be used throughout the majority of the song. Rhythms may change slightly during a chorus or bridge, but the meter will usually remain the same. Meters can be in 2/4 or 4/4, or 3/4 and 6/8 timing.
Make sure guitar and keyboard are in tune with each other. Play the first chord of the song on the guitar. Play the same chord on the keyboard. If they sound alike you have determined the proper chord. Write the first chord on your staff paper, using piano notation.
Repeat step 1 until all chords have been transposed or until you encounter a solo.
Determine the proper notes on the guitar. There are 7 major notes and several octaves on both guitar and piano. Sharps and flats will usually be determined by the key signature. If you don't know individual notes on the guitar, find the right starting note by playing the first note of the solo on the guitar, then attempt to find a match on the keyboard by playing different notes until you find a match.
Continue to play notes on the guitar, listening closely to determine what notes they may be. Play the same pattern on the keyboard, revising until it is correct. Notate the solo pattern on staff paper.
Add lines to delineate measures. Write words underneath the appropriate chords. Add any extra flourishes you would like.