Rule of thumb any time you're playing notes, and you hit a bad one:  No matter where you are on the fretboard, you are at most one fret away from a "correct" note.  i.e.  One that is in key.

Let's say you're going from G to D.  I'd use the second and third notes in the G chord and then jump right to D (the fifth).  If you're playing a blues song, use a flatted third.  That's a practical walk-up. 

Sometimes what I like to do is to jump to the octave, so I'll play a low G on the third fret of the E string then jump up to the fifth fret on the D string to hit another G and then use the flatted seventh, the sixth, and then on down to the fifth.  There's a practical walk-down. 

Another bit of advice is that if you play your walk-ups and walk-downs really fast and hit a wrong note that isn't emphasized, you can just shrug and say "That's the blues, baby.  That's the blues." 

Anyway, the point is that I pretend that the base chord from which you're changing is a scale, and then I use select notes from that scale - mostly the second, the third (or flatted third), the fourth, and the flatted seventh (and less often the seventh, but that has a very bright feel to it and I am usually playing bass for folk or blues and don't want so much of a "major" feel - it works good for Country though). 

I'm not saying this is "right".  I'm just saying it's what I do.

Hope that helps.  If not, a person with actual knowledge will be along directly to help you. 

- Zurf

Nela