Watch the Try Sometimes online guitar lesson by Jeff McErlain from Essentials: Chord Tone Soloing
Let's start with a basic two chord progression similar to The Rolling Stones song "You Can't Always Get What You Want". I've played this tune on many gigs, and it's fun to solo over. The chords are C7 to F, so we're technically in C Mixolydian. Whaaa? Don't sweat it!
Let's start with a C major pentatonic scale, which is C-D-E-G-A, and get comfortable with that. C major is spelled C-E-G and F major is spelled F-A-C. As we can see, all the notes of these chords are in the pentatonic scale except for the F. First concentrate on being comfortable using the C major pentatonic scale.