Let's take a look at the first beat in each of the bars below. See the triplet note grouping? Those are sixteenth note triplets, which basically have a span of six notes per beat. Make sure you palm mute that grouping, then immediately after play a quick eighth note strum with an upstroke. Once your hand falls back down on the strings, you'll then play two quick palm muted sixteenth notes.
Next comes the "alarm clock" part with the pinch harmonics. In the tablature, you'll see "P.H." markings to indicate the pinch harmonics. If you aren't very familiar with how to play pinch harmonics, check out Richard's excellent tutorial here. After each harmonic, slightly move your picking hand towards the fretboard so each harmonic gets a slightly different tone. It's supposed to be a bit random here so don't worry too much about getting the harmonics to sound the same each time.
Lastly, in bar 4 we'll end the riff with a descending chromatic power chord riff. Be sure to palm mute those power chords like crazy!
When you have it down, I'll see you on the next page for Exercise 2.