This is a great technique for guitarists to give a nice and smooth sound to their arsenal of guitar licks.
The idea here on this example is that you don’t use your right picking hand at all and you use only the power of your left hand doing a lot of pull-offs (flick the string with your finger towards the floor) and hammer-ons (smack down hard your finger on the string). When you combine both techniques collectively together is what we call a “trill”, especially when you start playing faster!
On this example I”m going up and down the strings using the E minor scale. It’s very easy to develop and it really gets the fingers moving all across the guitar neck!
I start with the E minor scale, switching afterwards to C# minor scale. The key here is to make these runs sound clean and smooth as possible while you use muting of both hands.
Enjoy and have fun!