My only two general rules when applying soft-edged camo are:
1) I always work from lightest colors to darkest. This ensures that the darker color is always on top and won't show through. Of course, if the camo job I'm trying to duplicate is dark to light, there's not much I can do about it.
2) Always allow each camo color to fully cure before applying the next color. I use enamels and this usually means I need to wait 24 - 48 hours between colors. It's well worth the wait in order to avoid any unintentional blending of the colors.
Hope this helps,
Foster