Free metronome: http://www.fretjam.com/metronome
Lesson page: http://www.fretjam.com/soloing-over-dominant-7th-chords.html
This video will help you explore several options for playing over dominant 7th chords, which are used in most songs.
Using C7 as an example, use the dominant 7th chord backing track to train your ear to the different colour tones each scale offers, with the arpeggio being the base or “skeleton” of your dominant seventh soloing.
Eventually, you won’t think in terms of individual scales, rather note selection – how, for example, the #4, natural 4th or b6 colours the dominant 7th sound.
To keep your bearings on the fretboard, keep those bass root note positions visualised in your mind. You can also see these root positions as good starting points for your dominant 7th soloing, literally building the scale around the chord shape.