The Spider is a bit more difficult than the other exercises, especially for your picking hand, since you have to change strings all the time. This makes it great practice for warming up and improving your technique for playing arpeggios for example, since they often involve only one note per string.

Each finger has its own fret and string in this exercise. Start on the low E string, on fret 1 with your index finger. Put your middle finger on fret 2 of the A string, your ring finger on fret 3 of the D string, and your pinky on fret 4 of the G string. Then reverse your fingers and come back down.

Practice this exercise all over the neck and using all sets of strings. When you feel comfortable enough you can also add some string skipping to further increase the difficulty of the exercise.