Let me recommend two sharp opening variations for the black pieces: the Sicilian Najdorf and Semi-Slav Botvinnik variation. They lead to dynamic and complicated positions with chances for both sides. They are excellent for playing for a win with the black pieces. To master one or both of these variations, I recommend getting at least one modern book per variation and study these in great detail. Also, check all grandmaster games you can find and explore the ideas for both sides in these positions.

The starting position of the Sicilian Najdorf is reached after

[FEN ""] 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6

Let's try to understand this position. Black has a statically better position thanks to the semi-open c-file. This means that an exchange of queens in this position is beneficial for black. White will fight for the d5 square and try to plant a light piece there. Black will try to deliver the d6-d5 center blow, thematic for the Sicilian system. White castles queenside in the sharpest Najdorf variations. Black castles kingside, queenside or stays with the King in the center, depending on the situation. Black chooses between the setups e7-e6, e7-e5 and g7-g6. White chooses between f2-f3 and f2-f4.

When white castles queenside, black attacks with the b- and a-pawns as well as the thematic exchange sac Rc8xNc3 bxc3, ruining the queenside pawn structure. If this exchange sac can be followed by picking up the e4-pawn, then it can be done at virtually any moment. Another thematic plan for black is placing a knight on e5 (after white's f-pawn is either on f5 or exchanged off) or c4 (attacking the b2-pawn and undermining the c3-knight).

The starting position of the Semi-Slav Botvinnik is reached after

[FEN ""] 1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.Nc3 e6 5.Bg5 dxc4 6.e4 b5

At first glance, black just grabbed the c4-pawn and is trying to hold on to it for dear life. Yet things are more subtle than this. Black has entered an assymetric position where white has to find dynamic plans to compensate for the material loss. It also looks like white is winning with e4-e5. Yet again, things are not so simple at all. A bit deeper we reach the following position

[FEN ""] 1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.Nc3 e6 5.Bg5 dxc4 6.e4 b5 7.e5 h6 8.Bh4 g5 9.Nxg5 hxg5 10.Bxg5 Nbd7 11.exf6

White will try to win using the extra kingside pawns. White can also launch an attack on the black King. Black will try to win by launching an attack on the white King, after developing with Bc8-b7, Qd8-b6 and O-O-O. White will most probably castle kingside, since staying in the center or castling queenside looks spooky. Black will open the a8-h1 diagonal and attack the isolated d4-pawn. I have used both these variations with joy and success. They are simply awesome!