How do I increase my chances to win as black in the Ruy Lopez? The Ruy Lopez is one of the most difficult lines for me to play against.  I just can't hold my position when I play as black. If I move 3... Nd4, I always get a draw at best, and usually take a loss. How can I improve my chances of winning in this situation?

EDIT : 
After I looked up the answers which were given to me, I found one solid win for black with the Cordel Defence that I found in Shredder Computer Chess if you insert this FEN to it.

[FEN ""]
1. e4 e5 2. Nf3 Nc6 3. Bb5 Bc5 4. c3 Bb6 5. d4 exd4 6. cxd4 Nce7 7. d5 Nf6 8. Nc3 O-O


Can someone show me, at which point does black take the initiative from white??

Thanks, 
Ahmad
The Ruy Lopez is probably one of the most analyzed openings in chess. You can find plenty of resources on the Internet. (Wikipedia's article on the Ruy Lopez is a good point to start).

I would recommend that you not go searching for "winning lines". You first need to understand the principles that lie behind each move of this opening. Once you have that understanding it is easier to examine variations and choose the one that best suits your needs.

For example, if you are an aggressive player and your chess level is average, you might wish to consider the Open Defense and the Marshall Attack.