Hey, heres a little exercise that I do using the Double Thumb 
technique. If youre not sure about Double Thumbing look on 
the net for some tutorials, sorry I couldnt try to teach some 
fundamentals in this tab. Well heres a little run through of it.

Riff 1

This is the little riff I play first. When reading this make sure 
that you take note off the Down and Upstrokes of the thumb represented 
by these signs. < = Down and Up = >. Lets give it a go.

       <         >
G|——————————————————|
D|——————————————————|
A|————0—h—3—h—5——5——|
E|——————————————————|

Play this riff as many times as you can start off slowly and then 
get faster and faster. When you get fast enough you shouldnt 
be able to hear the last 5 but you still play it. 

Riff 2

After a decent play of that move onto this.

        <        >
G|——————————————————|
D|——————————————————|
A|————0—h—5—h—7——7——|
E|——————————————————|

As you can see it just basically progresses up the fret board. 
Like the first riff start of slow and then got faster and faster 
until you cant hear the last 7.


Riff 3

Yep you guessed it.

       <         >
G|——————————————————|
D|——————————————————|
A|————0—h—7—h—9——9——|
E|——————————————————|

I think you know the drill by now. 

Riff 4

Sighhhhhh

        <            >
G|——————————————————————|
D|——————————————————————|
A|—————0—h—10—h—12——12——|
E|——————————————————————|

Well theres all the separate riffs. Got all those? Good, now 
lets move on. This a fun little diddy that uses all the riffs that 
Ive just showed you.

        <               >  <                >  <               >  
G|———————————————————————————————————————————————————————————————|
D|———————————————————————————————————————————————————————————————|
A|————0—h—3—h—5——5——0—h—5—h—7——7——0—h—7—h—9——9——0—h—10—h—12——12——|
E|———————————————————————————————————————————————————————————————|
And down
 
         <                  >   <               >  <         >
G|——————————————————————————————————————————————————————————————|
D|——————————————————————————————————————————————————————————————|
A|————0—h—10—h—12—12——0—h—7—h—9——9——0—h—5—h—7——7——0—h—3—h—5——5——|
E|——————————————————————————————————————————————————————————————|

There you go. Have fun. Try different strings practice and get 
faster and faster.

Thanks, Sam