You ever notice that when you truly know where you are going next on the guitar, things become almost automatic? What I like to do is always think of the next chord while playing the current one. Let's say you have a simple progression of I-IV-V in "G" (G - C - D) and the chords change on each new measure (in 4/4 time) like so:

[FONT=Courier New]
G------C------D
1 2 3 4 1 2 3 4 1 2 3 4 [/FONT]

Now, if you think about it *when* you have to switch on the 1st beat of each measure, you'll always be late. Instead, I like to "mentally" position my fingers on the third beat of the prior measure.

Just my $0.02 :-)

Scott