this is a game of mine 

 what do i have to do now after seizing that d5 central square?? often after i achieve my positional aim ( e.g get an central outpost for my knight ) , then i dont know how to convert the advantage into a win then end up in a draw...

any advice?? 

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EDIT  ( lol sry, actually there is a knight on d7 )

If you could manage but a draw from being a piece ahead, your problem isn't positional play, it's tactics.

Being up a piece like that, you shouldn't be in such a hurry to plant a knight on d5 (in that final position after Bxd5). Instead, use the half-open d-file as a lane of attack for your rooks. Your goal is to attack the backward dpawn and trade off pieces to a winning endgame. Now obviously you don't want your queen in front of your rooks like that, so it will have to move to say b3 for example.

Organize and conquer, don't chase. This means you use everything at your disposal for the common goal, especially since you know black will not be able to keep up in the long term to prevent it.

"I have him right where I want him! What do I do now?"

@estragon : actually there is a knight on d7 ( sry i forgot to put it ) , so if the position is like this, then what should i do??

firebrandx : thks~!! 

common sense. try to solve it yourself.

I suspected it was just missing, but where the Nd7 might be makes a big difference, of course.

First, let's assess the position:  White has a slight lead in development and more space thanks to his e4 pawn and the strong square at d5.  However, Black has ...Ne5 coming which should bring a favorable exchange, and he needs it to relieve his cramped game.  If White must reply Nf3xe5 dxe5 relieves Black of his backward pawn, his biggest positional weakness.

How to discourage ...Ne5 to avoid liquidating the weakness at d6?  There is no direct way to do it, and the Bc4, Qd3, & Nf3 all lack any productive move to get out of it.  So I would play the positional 1 a4-a5.  If Black reacts to avoid the additional weakness with ...b5  2 axb6 Nxb6, then White will have to either retreat the Bc4 or allow its exchange, but under better conditions.

In general terms, with more space and the opponent cramped, you want to avoid exchanges unless you get something to sweeten the deal, because exchanges make a cramped game easier to manage.