im no gm but i would play nc6. if i was black this would not only develop my knight which is a peice you want to develop early but it would put some pressure on the pawn on d4. im the type of player that i like to put pressure on the center asap as possible ;) and this would be the sort of move to do it. thats just what i would suggest but you have to think about what you want to accomplish and what moves are gonna get you there. good luck
A good response to 1.d4
Have you ever considered the indian lines/nf6? To play them there is a certain ammount of theory you need to know but they are very durable. 1...nf6 2...e6 or g6. If you want to stick to the more closed d5 you could try out the slav or semi slaw 1.d4 d5 2.c4 c6.
I've been wanting to play the Budapest Gambit (1. d4 Nf6 2. c4 e5) for quite a while now, but I just can't get anyone to play 1. d4 against me... It's not currently a GM favorite, but it's not actually unsound, and it should definitely be playable at your level.
I struggled for years to find something I was happy with against d4 - I tried more than half a dozen systems from QGD Tarrasch to Nimzo Indian to Grunfeld etc. Then I "found" the King's Indian Defence - this is an awesomely solid defence that gives lopsided positions for true winning chances. I am not saying, before anyone shoots me down that it leads to advantage, just the inherent advantage of giving me a position I am comfortable with and can fight from.
From here there are many theoretical options but as a pattern it is worth observing that black usually aims to play e5 and f5, expanding on the kingside and preparing an attack there. Have a look at some games with it and see if it hooks you.
I need a good response to 1.d4, at the moment I've been playing the queens gambit declined with 1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.Bg5 Be7 5.e3 0-0 6.Nf3 h6 But this seems to give black very minimal chance of actually winning the game, so I'm looking for a response that gives black some chances to actually win.
I'm not looking for an unsound gambit.
What could I play?