This is a great exercise that I've devised to make trilling easier. The fingering is 121212121212121213131313131313131414141414141414. Understand? You will in a moment. On measure six the notes are 14 and 20. Once you complete that move down to the 2nd string and start again, then the 3rd string until you can do it on any string. Then, move down a fret and repeat the exercise. Once you get to about fret 5 or so it should start to get difficult, if you can't make the stretch, STAY ABOVE THAT FRET. There's no need to hurt yourself trying to do this.