This first method is based on an idea I took from Greg Howe's playing and is a very 'open' and simple concept.
It's based on the idea that music is divided into simple phrases which are then combined into longer sentences. What Greg tends to do is to think in 4 bar sentences and creates his tension at the end of the sentence - almost like a cliff hanger in a cheesy Australian soap opera!
Lets say we're playing over an Am7 chord (as I do in the example videos) then we'd be playing an A Dorian scale as our primary harmonic source. Lets play this scale for the first three bars of our sentence (phrases) and in bar 4 lets use anything else that's unrelated to A dorian! 'What!?' I hear you cry! Anything? Well...yes. The idea is that you're creating some tension at the end of the musical sentence (bar 4) which you then resolve at the beginning of the new one. The less notes your chosen scale or intervallic device shares with A dorian, the more tension you'll get. I like a lot of tension so I chose to use an Eb Dorian scale in my video but anything will work if you resolve it well.
The real point here is that your phrasing and resolution must be good. If you just play a random scale with random phrasing and don't resolve your idea back into A Dorian properly then you'll just sound like you're playing wrong notes. Not ideal! In order to resolve well try to match the phrasing of your 'out' phrase with the 'in' phrase in the new bar 1. Also, try to resolve onto a chord tone - this will give you a strong resolution and guide the listener into the Am7 chord again after you've fried their brain for a bar! Think of it like 'call and response' but using two different scales.
Try all sorts of different scales and intervals for your 'outside' material. You may find you phrase more naturally with certain scale shapes rather than others.
Good luck with this - in the next video I've transcribed part of one of my improvisations using this very method.
Listen to modern Greg Howe or Wayne Krantz for more of this kind of playing.