I'm starting watching Heroes and I just watched the pilot. After watching it I read the first chapter of the graphic novel on the NBC page. But there's is 32 chapters of the novel published by now and there's only 21 episodes of the show to be aired yet.
So when (after having watched which episodes?) should I read each the chapters?

They usually upload the novels within 48 hours of the show airing.

#1 to 11 - correspond to the episodes 1 to 11

#12 to 18 - released during break #1

#19 to 23 - correspond to episodes 12 to 18

#24 to 29 - released during break #2

#30 to 34 - correspond to episodes 19 to 23

The first bunch of graphic novels filled in the blanks between the episodes. However, the later ones (I am not sure numerically), but around the introduction of Wireless, the novels started to give additional info that was not as closely tied to the episodes. These are in multiple parts so there will ultimately be more novels than episodes. You can be safe if you read a novel after each episode, but the novels which are in multiple parts can be read together, like the intro of Hana, her trip to the Pentagon, and the most recent multi-chapter "Walls".

Thankyou so much! That's exactly what I was looking for!

#35 to #51 were released during the summer break.

The latest graphic novel (Flying Blind) does not have a chapter number.

Someone should make a post of all the graphic novels linked in the order they happen chronologically, not the order they are posted.

I finished the one I've been working on for awhile. All info came from the heroes wiki, based on release dates.
SEASON 1
E: 1 - GN: 1
E: 2 - GN: 2
E: 3 - GN: 3
E: 4 - GN: 4
E: 5 - GN: 5
E: 6 - GN: 6
E: 7 - GN: 7
E: 8 - GN: 8
E: 9 - GN: 9
E: 10 - GN: 10
E: 11 - GN: 11
GN: 12 - 16
E: 12 - GN: 17
E: 13 - GN: 18
E: 14 - GN: 19
E: 15 - GN: 20
E: 16 - GN: 21
E: 17 - GN: 22
E: 18 - GN: 23
GN: 24 - 29
E: 19 - GN: 30
E: 20 - GN: 31
E: 21 - GN: 32
E: 22 - GN: 33
E: 23 - GN: 34
GN: 35 - 51
SEASON 2
E: 1 - GN: 52
E: 2 - GN: 53
E: 3 - GN 54
E: 4 - GN: 54b (bonus edition) ROGUE
GN: 55
E: 5 - GN: 56
E: 6 - GN: 57
GN: 57B (bonus edition) THE LAST SHANGRI-LA
E: 7 - GN: 58
E: 8 - GN: 59
E: 9 - GN: 60
E: 10 - GN: 61
E: 11 - GN: 62
GN: 63 - 103
SEASON 3
E: 1 and 2 - GN: 104
E: 3 - GN: 105
E: 4 - GN: 106
E: 5 - GN: 107
E: 6 - GN: 108