how do improve my positional play

and which books will help understand the najdorf for e4 reply , kings indian or grandfield I want to use this defence as they suite my style of play

If you want to improve your positional play I would recommend to think in every game; "where should this piece stand?". Many of the players that play positional make it as their playing style, but if you are more comfortable with attacking I would do that instead. For Najdorf :Starting Out: Sicilian Najdorf, Winning with the Najdorf Sicilian. Kings Indian: Modernized: The King's Indian Defense. Grünfeld: The Safest Grünfeld. This is what I would recommend.

Unless yourse a titled player, you have no style of play.  Learn the pawn structures associated with those openings, and you will understand why the pieces go where thye do.

I have tried many opennings and I had the most sucess with the kings indian for d4 I understand it concept and theme and I just want to get better at it...as for najdorf it gives me more of tactical play in the middle game

Positional Play:

Simple Chess, by Michael Stean [Overview of the main positional elements]

Judgment and Planning in Chess, by Max Euwe [More elements/excellent commentary and annotations]

The Middle Game in Chess, by Reuben Fine [Thinking process/evaluation/structural considerations]

Najdorf:

The Sharpest Sicilian, by Kiril Georgiev and Atanas Kolev [There are newer books, but this is still my preference for those "Najdorf days"]

The Cutting Edge 1: The Open Sicilian, by Milos Pavlovic

The Cutting Edge 2: The Najdorf Sicilian 6.Be3, by Milos Pavlovic

7 Ways to Smash the Sicilian, by Yury Lapshun and Nick Conticello

King's Indian:

King's Indian: A Complete Black Repertoire, by Victor Bologan

Grunfeld:

Not sure!

While I guess books related to specific openings can't hurt, they never seemed that interesting to me. Going through actual GM games with GM notes were often more helpful and fun for me. The key being figuring out why the Master made each move or described other lines in his notes. This might also help boost your positional play.

For the Sicilian Najdorf, Fischer's games in his "My 60 Memorable Games" might be useful. He also has more than a few KID's since both were his major defences for a long time.

For the Grunfeld, Botvinnik's book on the "Botvinnik-Smyslov Three World Chess Championship Matches" had some key formative Grunfeld theory games but also plenty of KID's.

Also, probably anything by a GM, especially the players themselves, for the 86 to 90 Karpov-Kasparov WC matches probably would have something worthwhile on the Grunfeld.

Read Positional Play by Jacob Aagaard.  It's from his excellent GM Prep series.

I felt compelled to blog about one of these positions just yesterday!

http://www.chessiq.com/a-very-instructive-position/

That book is great, but too advanced for the OP.

I am talking to Jacob Aagaard on faceboook at the moment, we are discussing the Bible of all things, awesome character btw :D

Agreed with Synaphai.  For improving positional play I take it one imbalance at a time.  Focus on games and positions where weak pawns or weak squares are the theme, open files, bad bishops, eternal knights, pawn structures, center types, space, and various piece imbalances.

 Also dynamics to convert one advantage to another, such as exchanging an active rook for a passive one (usually a bad idea) to enter a winning pawn endgame.