Being as free as possible to improvise and create on the guitar is a lifelong quest for most guitarists. The key is to expand the "familiar" and the usual. One doesn't have to reinvent what has already been done so well, but just know how to go farther - so to speak - with what has already been taught by great teachers as tried and true, and what the player him/herself has learned through experience.
This article assumes that the reader already knows how to play chords and single lines up to at least the fifth fret, or farther up the neck. Understanding of some keys in some positions is also assumed.
There are many approaches on learning how to expand one's knowledge of chords and the use of lines and arpeggios "on" those chordal passages, as well as playing guitar lines that are not necessarily about chords or modes and scales.
This Part 1 ( perhaps some subsequent parts as well) of this ongoing article focuses on the use of chords and lines associated with chords as a starting point of expanding one's knowledge of the fingerboard.
A very good way to begin expanding one's knowledge on the guitar (and music) is to take the approach of a keyboardist (pianist etc.). By this we simply mean that one should learn songs in such a way that one can play the melody of the song at the same time as the chords. In jazz circles, this is commonly called "chord-melody" - among other names. One can also call it "self-accompanied" versions of songs.
This way of playing is, of course, standard and the primary method in "classical" guitar playing. However, where classical guitar playing is "fixed," advanced "chord-melody" playing or "self-accompanied" playing of songs allows one to also create new versions of the written material at will, eventually leading to full on self-accompanied improvisation, meaning "soloing" in the solo sections of a song while playing harmonic clusters and lines - rhythmically or rubato - at the same time.
Besides the sheer joy of being able to make music like this, the guitarist also expands his/her knowledge of the great ocean of tonal music. The exploration of musical beauty, power and poetry is truly seen as limitless.
To conclude part 1, the reader and player is asked to simply pick songs he/she knows and find ways to play the melody along with the chords. The chords need not be played in full forms, but certain notes, such as the thirds and sevenths of the chords should be included if possible. Although maintaining thirds and sevenths are not to be set in stone, this approach usually maintains the signature sound of a chord. This is important because the progressions of the chords are according to the tensions and resolutions that the chord "sounds" bring about.