After you've had fun with the Fried Liver, you'll soon discover that experienced players don't recapture with 5...Nxd5, but rather play 5...Na5. Here are some games in the main line that will help your play.
Related literature
Complete Defense to King Pawn Openings, Eric Schiller.
Video on the Two Knights' Defense
New White Secrets against the Two Knights' Defense. GM Dzindzichashvili analyses the Two Knights Defense from White's perspective, concentrating on his new ideas in the system 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.d4 exd4 5.e5.