Lets start by assuming you know the seven classical scales, (Ionian, Dorian, etc.) And let’s assume you know the tritonic scales or the main notes in major and minor chords. There are many more combinations, and here are a few. First let’s start with the Flamenco scale. starting in A, the notes in the scale are A,Bb,C#,D,E,F,G#,A. This scale is obviously used a lot in Flamenco guitar.
Another good scale is the minor with a sharp 7th. This would go A,B,C,D,E,F,G#,A. Also called the harmonic minor scale. Then there is one I call three in a row due to the shape on the frets. This goes A,Bb,C,Eb,E,F,G#,A.
An interesting one is three frets apart all the way. this would go A,C,Eb,F#,A. Then you can take one note out of this creating A,C,Eb, A. You could also try removing the C or F#. A very alternative scale is the flat fifth scale comprising of only two notes, being A and Eb.
You might like to try this one: A,Bb,Eb,E,A. There are an almost unlimited amount of combinations especially when moving quickly from one scale to another over different chord changes. The classical scales are not the only ones that work just the ones the monks thought created the most heavenly music. While minor and major are undoubtedly the most common scales in all music. much of the pop music of the late twentieth century had vocal lines using the mixolydian.
Check out my other page on the classical scales and how to play them on the guitar using only the minor shape and moving it around to different positions. For example, B minor over the bass note of A is the Mixolydian, and following the notes of the A Myxolydian and playing the minor scale of each of those notes, A,B,C# minor etc gives you all of your classical scales.
As a final note, there are no wrong notes, and any combination can sound good to certain ears, and there are no wrong chords either. Please check out the links on this page, which lead to my free video guitar lessons, and keep practicing your scales.