There are two very simpleforms of improvisation that I teach guitarists.
the Blues Scale.NO1. FLAT3, 4 ,SHARP 4,5.7 OF theMajor scale. A blues scale against A major chord,Then same pattern againstSUB DOMINANT and DOMINANT,its a six note scale that can be used to improvise around.
then the pentatonic major scale, a five note scale[ more used in country rock or light rock]and also seems to work for a lot of American traditional material.