As a first experiment, try playing a succession of notes on the top string, starting
with i and alternating with m. Try to keep the notes even and matching each other
in sound. Then do the same thing starting with m.
Note that some players, particularly those specializing in flamenco, develop
a preference for starting single-note runs with a particular finger, usually i.
This is in fact counterproductive because the best finger for starting a run depends
on the specific passage.
Now try the second string, playing i-m-i-m-i-m-i-m, then m-i-m-i-m-i-m-i.
Finally, do the same practice on the third string.
After that, try the same exercise that you did with the left hand alone, playing
the first four frets of each string, this time with both hands.
When you reach the highest note, come back down the guitar playing the frets
in the order four, three, two, one on all the strings. This makes an excellent daily
If you try the string changes reversing the fingers, i.e., using i-m where I
have suggested m-i, you will find making the change from string to string harder.
This is a basic principle of fingering—where possible, we cross strings as shown
above. However, we need to be able to do it both ways, because the easy method of
crossing is not always practical.