1. e4 e5
2. Nf3 Nc6
3. Bc4 Be7
4. d4
your last move is too passive. haakan's Bc5 is a good defense. or Nf6. if you were protecting against Ng5, you dont need to, and the other 2 do anyway. ie:
3. ... Nf6
4. Ng5 d5
5. pxp Nxp
and the bishop is blocked from attack, and the knight is attacked. but then you have to deal with Nxf7, and bring your queen out.
and, if Bc5
Ng5 QxN
that move is still ok, but there are others that keep my advantage smaller.