Quite clever way to use the a6 knight to create threats on the kinside... took some time to spot. By the way, is there some particular reason to favour Bxd4 over Nxd4.
If one piece stands badly...

That's a really good question, about Nxd4, I really didn't spot that possibility, and Tal doesn't mention it in the book I got this from. So, I plugged it into an engine, and apparantly Bx is about half a pawn better :)

The Knight problem: if a knight can't get to f6 or f8 in one move, and likewise for white, f3 and f1, then mate is on. You might want to remember that when deciding which piece is best to take.
My Problem is also same as Mephisto's. I think we average players suffers from this, what I call this problem is "NOT ABLE TO EXPLOIT THE SLIGHTLY BAD POSITION OF THE OPPONENT". Take it like this,
if you have a Knight extra- You can win easily
Two pawns extra-you can win but with efforts
One pawn extra-win is not guaranteed
As your elo increases your ability to win with slightest advantage increases.When I began playing chess I remember losing even a rook ahead.
So, the best way is take any game position when it is reaching endgame take any 2 pawn away from one side and pplay the position with strong computer and win.
This is what I do to practice " Winning a won game".

Nice puzzle and also im playing a game where I did a similar thing with the queen and the only way to stop mate was to push up the pawn thus getting the bishop
this is the link: http://www.chess.com/echess/game.html?id=40175758
Move 15-19
.... the entire game is bad, said Tarrasch.
Can you find a way to take advantage of the poor position of Black's Knight on a6
?Henkin - Lebedev 1961