I'm a big fan of playing outside and use various methods to achieve this. i.e. sometimes melodic minor, or altered scale, sometimes just half step below resolving back up ( or back down if half step above) or sometimes diminished lines.
Thing I'm not 100% on is when to use outside stuff. Pretty clued on re blues and find that major blues works great for outside stuff (better than minor) and that generally I make outside playing work as the chords change particularly from I chord to IV chord or on the V chord (this works great as it resolves down to the I chord)
Also pretty obvious in jazz e.g. ii v I progression, particularly in minor, when you can use altered scale for example.
However, i'm less clear in more conventional music i.e. rock and pop. Sometimes I try outside stuff in these genres and it just doesn't work, sometimes it does.
Can anyone give clarity as to when outside stuff works and when it doesn't?