Along with a perfect neck knowledge, I consider it essential a good rhythmic coordination, i.e. knowing how a rhythmic group sounds and feels, and having it at your disposal under your fingers.

The following exercises must be executed to a metronome, beginning with a speed allowing max precision (like, slow, maybe).

You can use a single note or an open string:

1) 1 note per click (metronome beat): quarter notes

2) 2 notes per click: eighth notes

3) 3 notes per click: triplets

4) 4 notes per click: sixteenths

5) Combinations:  from a group to another without stopping. 

Permutations are:

12 / 13 / 14 (one to two, one to three, one to four)

23 / 24         

34

We can introduce quintuplets and sextuplets (five and six notes per beat).

Permutations:

15 / 16

25 / 26

35 / 36

45 / 46

56

Let's consider three rhythmic groups combined:

123 / 124 / 125 / 126

134 / 135 / 136

145 / 146

156

Four groups (some examples):

1234 / 1235 / 1236

1245 / 1246

1256

1345 / 1346

1456

Now let's apply these exercises to scales: the purpose is being able to play any scale with any rhythm group.

EXAMPLES:  Major scale, eighth notes;

Major scale, triplets (below):

Major scale, sixteenths, 3 notes per string: 

As above, let's use combinations of rhythms, to make the scale less predictable.

Major scale, "2+3":

Major scale, "2+3", repeating:

Another use of this study is to apply it to power chords: combinations will give interesting (progressive, in a way) rhythmic groupings.