In this video
We learn "Joker and the Thief" by Wolfmother. This riff can seem pretty daunting at the start, but this is such a fundamental and simple technique. When you get it, there is absolutely a knack to it. I'm going to talk you through that knack now. Just learn it slowly and speed it up gradually over time, and you'll be amazed at the lead lines and riffs this enables you to play.
The Hammer-On Technique
We're going to be picking the middle two strings - string four and string three. The picking hand doesn't do any more than this - it's going to pick string four then string three. The fretting hand does all the work, and it does literally a hammer-on technique where we pick string four and you can hammer on with your fingers to actually get the sound of a note. This is made easier by having plenty of overdrive (gain) on your amplifier, which gives us the sustain and enables the notes to ring out much easier.
Setting Up
Have your fingers and hand ready as if you're playing E minor pentatonic position one. We're going to be ready to hammer on the first finger at fret five on string four, then fret seven with the third finger. These are the strongest fingers of the chord playing hand because they've been playing this minor pentatonic scale perhaps for quite a while now. Pick string four, hammer on the first finger, hammer down the third finger.
Warming Up
As a warm up, many people need to warm up each finger individually. Pick the open string, hammer on the first finger - we can't do anything without that first finger hammer-on. Then do the same thing with the third finger at the seventh fret. When we hammer it down, good positioning is still everything. We want to be this side of the fret, not that side, and we want to make contact with the string at the same point as you would if you were playing a chord. It wants to be just on the tip - fingers curled over like a claw hand.
The Full Riff
The second half of the riff is the same thing but a string down. Pick string three, hammer on to fret five and seven. It's crucial that we get everything ringing out in those notes really clear at that slower tempo first, around 50% speed. The hammer-on notes need to sound the same loudness as the open string picked note. Once we get this flowing and start to build speed, we can relax more. Keep them all evenly spaced with no pauses. Join in with me nice and slow, and then speed up gradually. In the intro I did a loop of that using the looper pedal, then played the power chords D5 and C5.