Originally posted here by Double//Cut
chmod permissions 755 etc etc are based on counting

read = 1
write = 2
execute = 4

want the user to have Read Write Execute, 1 + 2 + 4 = 7
want the group to have Read (NO)Write Execute, 1 + 0 + 4 = 5
want everyone else to have (NO)Read (NO)Write (NO)Execute, 0 + 0 + 0 = 0

== 7 5 0

chmod 750 <file/dir>

other examples

want the user to have Read Write (NO)Execute, 1 + 2 + 0 = 3
want the group to have Read (NO)Write (NO)Execute, 1 + 0 + 0 = 1
want everyone else to have Read Write Execute, 1 + 2 + 4 = 7

== 3 1 7

chmod 317 <file/dir>

As being specific to Apache, on a production server, i couldnt say but
while doublecut has most of the explination correct, there is an error

read = 4
write = 2
execute = 1

source: http://en.wikipedia.org/wiki/Chmod

other than that, everything is sound