Go for as smooth a tone as possible, with not too much treble. Set your amp to ‘just breaking up’ then add boost or overdrive to provide the required amount of gain. This will help the notes sing. A compressor placed at the front of the pedal chain will add further smoothness and sustain. Lastly, reverb or long delay will bring a studio quality to the sound.
Steve Vai is one of the great legato players of rock guitar