This is the classic first exercise to practice on the guitar to improve your speed and warm up both your hands. Play it slowly then increases the speed, but if you find mistakes then slows down it again. Use a metronome at 60 bpm and play 4 notes a beat, If you can play it without mistakes then you can increase of 4 bpm. Pay attention to the direction of the picking, from above (downstroke) or below (upstroke V)