This is a rich, difficult position that will reward some study time. Presumably you see that White has the kernel of a discovery on the f-file. You also see a natural way to execute it: 1. Bc7, attacking Black’s queen and also threatening 2. Qxf7+. But you wonder how formidable the latter threat really is. Suppose Black replies to 1. Bc7 with 1. ...QxB, allowing White to carry out Qxf7. Now Black’s king is forced to h8—and then what? Your queen can do no more by itself from f7. The key move to see is 3. Rh4—a fresh mate threat (Rxh7#) against Black’s king on its new square. Black has a move he can spend responding to it but there is nothing he can do to avoid trouble. He can’t get any of his pieces to h7 to defend the square. The most he can do is advance his h-pawn. The first possibility, 3. ...h7-h6, doesn’t help: it results in 4. Rxh6+, BxR; 5. Qh7#. Black's second option, 3. ...h7-h5, is a little better as it avoids mate. Play goes 4. Rxh5+, g6xR; 5. Qxh5+ (always looking for the next check), Kg8; 6. Qh7+, Kf8; 7. Ne6+ (forking Black’s king and queen). The net: White gives up a bishop and a rook to gain a queen, three pawns, and a better game (his offensive continues; there are various ways he might win still more material).
Assuming you follow all this (it's worth a patient look), what does it prove? Just that if Black replies to 1. Bc7 by playing QxB, he gets hurt; so Bc7 does indeed give White a working discovered attack. But what will Black do about it? Obviously he doesn’t want to simply forfeit his queen; does he have anything better? Ideally he would like a move that makes a good counterthreat against White while also defending against mate. Black almost has such an option in 1. ...Ne5, attacking White’s queen and guarding f7. Of course it loses the piece to BxN, but it’s still Black’s best reply.
This position contains a couple of natural “stuck points”—places in the analysis where it’s easy to hit a wall. The first comes after you see 1. Bc7, QxB; 2. Qxf7+, Kh8—and now it needs to occur to you to bring the rook over to h4, which is tricky to see for several reasons:
(a) Rh4 brings a piece into the action that had not initially appeared to be part of the plan. It’s natural when you begin playing with a tactical idea to focus on the principal pieces involved—here, White’s queen, bishop and knight. But as we recently had occasion to note, many a sequence turns out to depend precisely on the clever addition of an unexpected piece or pawn to the attack. This is a key reason why developing your pieces (i.e., getting them off of their original squares) is important before launching an offensive. They all may have the potential to perform supporting roles. The repeating moral: think about all of your pieces and how they can help when planning a tactical sequence.
(b) Rh4 requires you to remember that the bishop now on f4 would be gone after the first move and that this would open a line for your rook to use to reach the h-file. This is a standard sort of cognitive challenge at the chessboard. The only cure is to be careful about it when you practice visualizing these sequences: every time you make a move, think not only of the piece on its new square but also of its absence from the old one.
(c) Rh4 is not a forcing move in the strong sense associated with a check or capture, so it might not spring to mind as quickly as those other possibilities would. But it still requires a look because it creates a mate threat: it aims a piece at a square next to the enemy king that you already have under attack. It therefore forces Black’s reply; it makes him advance his h-pawn, which ends up having other consequences as well. Moves of your heavy pieces (your queen or rooks) to the h-file against the castled enemy king are common sources of good, forcing threats.
A second natural stuck point comes after 3. Rh4, h7-h5; 4. Rxh5, g6xR; 5. Qxh5, Kg8; 6. Qh7+, Kf8. At this point you need to see 7. Ne6+—the knight fork. You might overlook it by thinking in a rut. You have been trying to chase down Black’s king with your queen; now you have run out of ways to do it. The earlier point repeats: when your idea hits a wall, remember to ask afresh how your other pieces might help, and whether some new tactical idea might make an unexpected appearance. This is especially important when you have a knight in the vicinity and the enemy king is moving; the potential for a knight fork may pop up at any time during a sequence. (And of course you have to remember as well that at this late stage of the sequence Black's queen still sits on c7, where it went on Black's first move.)