I'm an amateur guitarist so I could never do this on stage, but do any guitarists here ever improvise a solo? I know the technique is more common in rock, blues, etc. But I would like to see it used a little more in metal.
....it's used all the time in metal. All those bands that do the live guitar/keyboard battles are improvising.....and Dream Theater does more improvising than I can count.
really you could be like slayer and improvise every solo you have lol and not know shit about what you are doing, just crank the wang bar and go by "feel" or you could learn theory and scales and do some shredimprovisation
Learn
Major - and all its modes all over the fret board pick 2 keys of major and learn all the connected modes
Minor Harmonic
Melodic Minor
Pentatonic Minor
Blues
Pentatonic Major