Pick the right notes for the right chords and sound like a guitar genius...

A common question from beginning guitarists is how to choose an appropriate scale to improvise with over a particular set of chord changes.  Maybe you've gotten your minor pentatonic down, drilled it into the ground, and you're ready to move on to some new challenges.  There are a few different ways of thinking about scale choice.  I'm going to present my favorite way, which involves the least thinking.  Thinking damages music performance.

First figure out what key the song is in.  This gives you your basic set of seven notes that will work as home base.  If you're working with standard notation, take a look at the key signature.  If you don't have that available, look at the last chord of the song.  That usually will the be the root of the key. 

Let's use the example of F major.  The chords in that key are F  Gm  Am  Bb  C  Dm  Edim.

Those are called the "diatonic" chords in the key of F major.  That means all the notes in those chords appear in the scale and don't include any outside notes.  So you can play an F major scale over any of those chords and you're safe.

You may discover that some of the notes don't work as well over particular chords.  Use your ears to decide which notes sound good or not to you.  Theoretically all of them work.  It's just a matter of how consonant or dissonant you want your melody to be.  Over the Gm chord a Bb will work perfectly, a C less so.  But it works as a chord extension (Gm add4), which is fine too.

Right now you want to shoot for chord tones because that will be the easiest way to create a melody that sounds good immediately.  That means over the F major chord you want to play the notes F, A, and C.  You can, of course, use other notes, but those three will fit perfectly.  Fill in between with other notes, but hit your chord tones in important places, like beat 1.

Let's go a step further.  Say you have a chord progression like this:  F  A7  Dm  Bb.  Which of those chords is not diatonic to the key of F major?  If you said A7, good job!  There is a C# inside that chord that isn't included in our scale.  That means a regular F major scale won't work as well over that A7 chord.

There are two solutions here.  You could just avoid the C altogether when you get to that chord.  But frankly that's not as interesting.  A better way is to swap out C for C# in your scale whenever you get to that A7 chord.  That's going to make your melody line track more closely to the chords, sounding glued to it, and more interesting to the listener.

To practice this, isolate just the two chords F and A7 taking a measure or two for each.  Practice soloing over just those two chords until you get comfortable switching the C to C# and back each time.  Then you can drop it back into the rest of the progression, which is regular F major.

Here's your action steps:
- Find the home base scale you can use for most of the piece.
- Pick out the chords that contain notes from outside that scale
- Find the notes in those chords that you can pinpoint as they go by

Now we've taken a lot of the stress and thinking out of soloing and you can concentrate on creating fantastic melodies.  As I mentioned, this is only one way to think about it.  But it makes for a good simple entry point to the ideas.