Watch the Improvising over a Jam Track Shape 1 Overview online guitar lesson by Rob Garland from Melodic Soloing: Major Scale
Here we're making melodies over a chord progression in the key of C improvising over the jam track. The chords are C-Em-Am-G, and the tempo is 115 BPM.
This is a I-iii-vi-V progression in the key of C, therefore all the notes in those chords are diatonic, meaning they are from the C major scale. I'll improvise creating melodies using Shape 1 in the demonstration video then you should try it.
Phrasing Tip: Come up with a melody/theme based around just a few notes and try to repeat it as the chords change, embellish it, and change the rhythm, but do it remaining inside the shape.