This blog gonna show you the easy way to do for how can you unblock someone that you blocked before.
haha I just make this blog because one of my friend's boyfriend block me in his Girlfriend facebook account hmmm jealousy ha :D
ok First first Log in to your facebook account then find the Privacy Settings under the account button (Of course you'll have to click first the Account)
then after that. like what you see in the picture below, just Click the Edit your list (Circled by color red)
after that you will see the list of people that you blocked. and that you just have to click the Unblock link, after that you will be able to see his/her complete profile again. (but that is weather when you are friends or not)
I hope I helped you... :D