On the journey that is guitar, there are certain observations you make over time.  Over these many years, and after learning how to play countless guitar solos, one thing above all else has become abundantly clear. Most soloists use chord tones during their solo.

What is chord tone soloing?
Well, it is exactly what it sounds like. It is using predominately the notes, that make up the chord you are playing over, in your solo to make melodies. So, if you are playing over a C Major chord: The notes in C Major are – C, E, G. Therefore, if you are soloing, what 3 notes on the neck do you think will likely always sound good?

You got it! C, E, & G!

For you advanced people you would probably say “Well that is just an arpeggio*?” To which I would respond “Yes it is!”. I have always maintained, that for actual application, arpeggios are actually far more usable than scale forms to the beginning soloist. But that discussion is for another day!

So how do I use this?
OK, down to the nitty-gritty! Let’s say you have the following chord progression:

|  C / / /  |  G / / /  |  Dmin / / /  |  C / / /  |

This progression is in the key of C, so theoretically any note of the C Major scale will work over this.

Here is the scale form for C Major. The darker circles form the scale pattern.

However, for this chord-tone approach; over the chord C you would want to stress the notes – C. E. G. For the chord G you may want to stress the notes – G, B, D. For the Dmin chord you would want to stress the notes – D, F, A. All these notes reside inside the C major scale.
As the progression passes these notes of the scale should “light up” in your mind. These notes represent home-base for each chord if you will. They will always sound good for the beginning, or more importantly, the ending of your phrases.
Here are the 3 chords in their “lit up” state. The coloured notes are your chord tones for each corresponding chord.
So why wouldn’t I just save time and use the C Major scale for all 3?
Sure you can, that is one approach and it is MUCH easier. But herein lies the crux of why most  players don’t learn this. It takes work to not only learn the scale form; but then learn how each chord within breaks out of the form. It is this “work” that is the gate between many, and the promised land of melody we all seek. If you can do yourself one favour, do this: stop looking for shortcuts! Face the work head-on and you will get there quicker. Take it from the KING of all shortcut lookers. Let me help save you the wasted time. Rant over : )
Consciously changing your notes, with the chords going by underneath, takes a lot of practice to get smooth at. But trust me, you will get better at it, once you begin approaching it this way. The first time you try, you will think “this is WAY too hard” and many will give up. But I urge you, for the good of your playing and for all those that will listen to you, forge onward. It WILL get easier with each passing session.
OK buddy, you got my interested … now inspire me.
Honestly I could post many examples of famous players doing this for your listening pleasure… but I won’t. I will do one better! One of my favourite all-time guitarists, is the masterful David Gilmour of Pink Floyd. Known for his melodic singing-style solos.  Over the years, I have had many students eager to learn how to play the way he does. There is one element to David Gilmour’s playing that many fail to recognize – he uses chord tones constantly. He is ALWAYS addressing the chords.
The following is an analysis of the first solo in Pink Floyd’s classic song ‘comfortably numb’. Take a look at how often David hits chord tones in this very cool solo. I have coded the chord tones in colour, with their corresponding chord above. I believe, he views each chord change as almost a key change… with minor pentatonic lines mixed in.
As you can see at a quick glance, there are more coloured notes than non-coloured. This demonstrates the power and melody that chord tones can bring your solos. Actually some of the non coloured notes are the 7th’s! So if we extended out the chords by one more note almost all of them would be labeled. (Remember as you look at this, when you bend a note, it is now a new note regardless of the fret number – a full bend is the note 2 frets higher and a half bend in the note one fret higher. )
For an up close video of the both solos in the song, click here to see this post
Is it the only way to solo? Of course not. But it is certainly a skill all advanced guitarists have. As I said in my rant, there truly is no one-size-fits-all solution where music is concerned. Some players do all of this by ear. Many dont realize they are doing it… they just think that note sounds “cool” over that chord. OF COURSE IT DOES YOU FOOL! It is most likely part of that chord.
This approach is not genre specific. Rock, Jazz, Country, you name it. The chord types change but the principle of the approach remains the same. Do yourself a favour and get this skill in your pocket. You will be glad you did.

Then send me a cheque : )

* from wikipedia: In music, an arpeggio (plural arpeggi or arpeggios, or known as a broken chord) is Italian for broken chord where the notes are played or sung in sequence, one after the other, rather than ringing out simultaneously.