It's easy and sounds great as a turn around.
Let's say you play a progression in E minor, something like:
I - VI - IV - V (Em - C - Am - B[maj])
You can spice it a bit by adding the fifth chord of the fifth !?!?
Example: The V of the Em (I) is Bmaj of course (Harmonic Minor).
The fifth note from a Bmaj scale is F#. So the if we play a F#maj(7) before the turn a rond Bmaj7 we get a different kind of sound wich also allows us to play the E melodic minor scale (Ascending) over that particular chord.
So the progression now whould be:
I - VI - IV - F#maj7 - V
You could also see het as the 2nd note from the scale in major(7) form.
So if we would have the Am scale which has a B as second note. You could play a Bmaj(7) before the V.
When you play this, you will love Bach.
