This simple exercise will help your hands learn how to communicate better. If either hand is out of sync with the other, this will sound like S#@T. Practice slowly, and build up speed after you can play this very cleanly.

Play the first four notes ascending with your fingers over frets 1,2,3,4. Then shift up one fret. Play the second four notes descending with your fingers over frets 2,3,4,5. Shift up one fret. Play the next four notes ascending (like the first 4 notes) except over frets 3,4,5,6.

Your left hand finger pattern should always be 1-2-3-4-(shift)-4-3-2-1-(shift)-1-2-3-4-(shift)-4-3-2-1-(shift)-1-2-3-4-(shift)-4-3-2-1-(shift)-etc, etc.
This example is written on the D string, because I found this is the most comfortable string to begin on. Once you get the hang of it, practice it on all 4 (or 6 if you have them) strings. It would seem that all strings would be the same...so what is the big deal?? Each string has it's own feel, and your left/right hands are hitting the strings at different angles. Each string requires its own practice.

Good luck, and have fun!