Any hints on how to be a more aggressive player. I tend never to put my opponent into enough pressure and I often lose according to that.

I believe 21. Be7 is stronger.

21... Qg8 22. Qxd7 where the Bishop is also hanging

21... Qe8 22. Nd6 distracts the Queen from the defense of the Knight

21... Qc7 22. Nd6 where the Bishop is immune due to 22... fxg4 23. Nf7+ Kg8 24. Nh6+ Kh8 25. Qg8+ Rxg8 26. Nf7#

17 bxe6 seems to win pretty much on the spot. 

14. Nd6 would have been interesting!

I think 24. Bxf8 would have won the knight.

14. Nd6 probably wins as it wins a pawn and destroys the king's castle after

14... Rd8 15. Nxf7 Kxf7 16. Bxe6+

Have you done much study on determining which are best candidate ideas or moves and calculation?

oh and 21.  n-g5

 

The queen is forced to capture the knight(otherwise a smothered mate or a fork of king and queen) when you get to take the knight on d7 and you are simply up a rook as opposed to an exchange. 

 

As to the question of how to become more attacking.  Work on tactics and sacrifices.  The more motifs you know the more easily you will be able to crack a defender.  It will also be easier to recognize what type of atttack will work BEFORE you start the attack.