Main thing is, and this is a must, do NOT prewash your fabric. Prewash shrinkage causes the print patterns to mutate and you'll find it impossible to match the prints up.
I think most people use a 60 degree triangular ruler or the 60 degree line on your straight ruler. Personally I've always used the straigt ruler.
However, I've seen some 4 patches made with large prints or border prints that end up looking similar to Hawiian applique.
Experiment around until you come up with something that you really like.