1. d4 problems

I am having problems preparing against 1. d4 as Black. For a while, I have been using this "system" opening that's not really great. It works OK against lower-rated players, but not against higher-rated players, when I get absolutely no play. I need to find something that gives me at least some winning chances against higher-rated players. I have a book on the King's Indian Defence, but there are a lot of lines in the KID and I don't think I have time to learn it and get some experience before my next tournament. I am looking something (anything at all, really) where I can learn a few lines and just get a playable/easy position.

Right now I am looking at the QGD/Semi-Slav and the Slav. Thanks in advance!

(BTW please don't use my online blitz/rapid games to estimate my OTB classical playing skill, which is higher.)

what is the systemopening you have been using?

It's basically: play ...Nf6, ...c6, ...d6, ...Qc7, ...Bg4, ...e5, ...Be7/d6/c5, ...Nbd7 and then castle either side, but Black gets no play out of it. It works fine at 1600-1700 level or lower, but any higher than that and White is too smart to let you get much of a chance.

King's Indian, Nimzo Indian, or QID

The QGD is your best bet as it's the least theoretical way to get a good position against 1.d4, and it's equally effective against 1.c4 and 1.Nf3, unlike some other options like the Grunfeld or Nimzo-Indian. You have to have something against the Blackburne QGD, the Exchange Variation, the Catalan and the mainline.

I can only concur with the last two posters, go for the QGD. It's withstood the test of time for well over a century. Select a good book, such as Drazen Marovic's 'Play the Queen's Gambit' (despite the name it covers both sides very objectively), or Matthew Sadler's books on the QGD, and then you'll be perfectly set. In my view, you're better off picking Marovic than Sadler, for the simple reason that Marovic has a much greater natural feel for this opening than Sadler (who tends to be unfairly dismissive of some important variations, such as the Lasker Defence - still played at the very highest level with good results for Black).

Try Grunfeld Defence or Benoni Defence or Benco Gambit and you'll start winnig every second game when your opponent plays 1. d4

Why? These openings are not better than the simple Queen's Gambit Declined, but are harder to learn.

Because they require a special knowledge to play against them. If you will just develop your pieces as usual against Grunfeld Defence - you are going to lose the game very "painfully".

Are you sure?

I'm sure if you'll accept the Grunfeld Defence by playing this variation:

If you won't play it then it will be quite easy for Black to equalize the game and to have a solid position.

What is the GQD? Gambit Queen Declined? Grand Queen Defense?

Hahahaha! My apologies, Queen's Gambit Declined, was what I meant!

grunfeld. you don't have to memorize too much lines, just read the main line and understand the idea of it's counter attack strategy.pressure on d4!pressure on d4! more pressure on d4!

The Grünfeld is probably one of the hardest openings to master thanks to it being such a dynamic opening. The OP said he was looking for something he could learn relatively quickly and easily get a playable position.

"grunfeld. you don't have to memorize too much lines" This is absolutely not correct; you have to memorise possibly more lines than in any other opening against 1.d4. Black only gets pressure on d4 if white cooperates - I already pointed out several lines where black has to alter his approach. Here are some more ideas:

The lasker defence in the QGD might be the best for you, it has less lines to study than the Orthodox or Tartakawer and dissuades white from trying sharp lines against it. the one but against it is that you will need good endgame technique to score with it since you are trading two pairs of minor pieces at the very least.

For something somewhat different that will result in fun games that is easy to play try the Leningrad Dutch. It is basically a system for black (though white has a couple of sidelines such as 2. Bg5) that gives a sharp position but has simple ideas and is fun to play.

This is the "mainline" position of the Leningrad, in which black will try to play an e5 push and take over the center and then put pressure on white's king, and white usually aims to attack on the queenside. You just need to know a couple of ideas and you're set, very easy & fun to play 

Sorry I didn’t explain it clear. But it’s all my personal feeling and personal experience. Grunfeld is truly difficult and complex and dangerous to both sides AT PROFESSIONAL LEWEL 

But in AMATEURS GROUPS,I think it’s definitely okay because grunfeld, though can be the most changing ,its mainly strategy is easier to understand: restrain the central pawn, side wings attack,queen side pawn majority. I think it’s much clearer than KID,and even than QGD maybe.

 I played Grunfeld all the way from 1600 to 1900 ,and I only read 1/3 of two books ( I mean 1/3 of each,I didn’t finish either of them).

Yet I could be absolutely wrong,but what I wrote is really what I felt and what I want to share @(o･ｪ･o)@

Another relatively easy line to play is the Queen's gambit Accepted, which is rare in amateur level since it's supposedly a "bad" move but in reality is quite playable.