You can do it a zillion different (hotly contested by internet beer nerd ) ways. When using a secondary, in my opinion and experience, it is best to transfer and then wait until you are 4-5 days out from bottling/kegging before dry hopping. This way you get the freshest aroma and none of the "grassy" flavors some people associate with extended dry hopping.
So, if you secondary for a month wait until the end to dry hop, but if you only secondary a few days then go ahead and throw the hops in. Still, read around on the forum as I'm sure there is considerable discussion on this sort of thing. Luck.