|Turn the RJ-45 end upside down so that the little locking lever is on the bottom. Look at the wires in the end. An A standard should start with Not Green/Green on the left hand side. B would of course be Orange.|
When you know which way the end is punched, then do the keystone with the same standard.
The keystone should show you both the A and B standards. If it doesn't, get one that does. The following link to a page that shows an RJ-45 keystone will give you an idea of how the A and B standard color codes are usually put on an outlet so you know what to punch where.
The following wickipedia Cat 5 page is actually a pretty good resource so give it a look and read.
Don't forget to test the cable when you're done!