A bass player once showed me a spider exercise and it went like this :
1st finger on the B string 1st fret (C) then 3rd finger on the E string 3rd fret (G)
2nd finger, B string 2nd fret (C#) then 4th finger-E string 4th fret (Ab)
3rd finger-B string-3rd fret (D) then 1st finger-E string-1st fret (F)
4th finger-B string-4th fret (Eb) then 2nd finger-E string-2nd fret (F#)
I hope this made sense :oops:
It really stretches your fingers especially when you begin to skip strings for example, instead of B & E you can go B & A, B & D, or B& G with the same fingering. Also, I like to go up and down the fretboard for more exercise.