e4 e5 f4 bc5 is the most famous line of the King's Gambit
King',s Gambit declined Bc5
How can u play d4 for white? Like this?
U just go into a kind of scotch where f4 weakens your position, and e4 will be a target (Qe7 instead of 0-0 is alos sensible).
Or like this?
So no sorry, Nf3 and d4 is not a good set up for white in king's gambit declined.
If u really want to achieve d4, then u have to play c3 before.
Like this :
It is less clear, though i prefer black : white will establish a strong centre with d4-e4 but black will hit it, with Nf6, Bg4, Nc6 (move order can change, and the main variation on c3 is Bb6).
Nowadays (as in Rubinstein's times...), the main variation begins after this :
But as i said, it is just the beginning of the story, and black as alternatives before, like a6 (making a room for Bc5 in case of Na4) instead of Bg4...
If u want more informations, just purchase some excellent books on this opening.
As black, beating the open games by Mihail Marin is the reference.
As white, i like very much The king's gambit by J.Shaw.
Nf3+ d4 should be good for white