I too strongly agree with the prior answers. However I've decided (and this might prove to be unpopular) to answer the OP's question to the best of my ability. If the OP or any other viewer wishes to ruin their experience by skipping the first few books, then that's up to them. I will however spoilerify the whole thing to protect the innocent. There are way too many differences to list, and too many minor characters, but I shall endeavor to list the most important ones. If I miss any, tough luck. Physical differences (Daario's blue beard for instance) I will not list.
Last chance to leave before you lose your ASOIAF virginity in the worst way possible. Even with this ham fisted guide, you will lose many of the nuances and subtleties of the books. You will also lose much of the history of Westeros before the events of the story.
Things you need to know if you wish to skip book material leading up to the end of Season 3:
Q. Where do I start reading?
A. There is no clear cut place you can start, but Book 3 "A Storm of
Swords" Chapter 39 "Tyrion" (page number varies by edition) is as good
as any. There will be some overlap with the TV series, but that's
Q. What character changes do I need to know to start reading?
A. Here's a quick guide:
Ros: Does not exist in the books and is an amalgamation of several prostitute characters, chiefly Alayaya.
Yara Greyjoy: Is called Asha Greyjoy in the books.
Aeron Greyjoy: Book only character. Theon's uncle. A once playboy, he later discovers religion and becomes the head priest of the Drowned
God faith. He is called Damphair by his followers.
Ser Barristan the Bold: Is disguised as an old squire called Arstan who squires for Strong Belwas. He has not yet revealed his
identity to Dany.
Strong Belwas: Book only character. A eunuch gladiatorial warrior who joins Dany along with Ser Barristan.
Loras Tyrell: Is not the only Tyrell son. He is the youngest son after Wylas Tyrell (a lame legged scholar) and Garlan Tyrell (a
skilled knight who is better at swordsplay than Loras).
Pyp: TV Pyp is a combination of book Pyp (mischievous prankster ranger) and Dareon (singer who was sent to the Wall because he refused
the sexual advances of a lord).
Thoros of Myr: TV Thoros is a combination of book Thoros (a priest of the Red God who lost his way and has now regained his faith) and
Tom o'Sevens (a fun loving bard).
Talisa: There is no Talisa in the books. Her counterpart is Jeyne Westerling. See below for more on her story.
Shae: Book Shae is not nearly as well explored. In the books Shae comes off as mischievous (without the mean streak of TV Shae),
spoiled, and an obvious gold digger. She never called herself Shae the
Dagmar Cleftjaw: While he was still an underling of Theon, he never joined him in Winterfell. The role taken by TV Cleftjaw in
Winterfell was done by Reek in the books.
Donal Noye: The Night's Watch smith and a mentor of sorts to Jon Snow.
Kevan Lannister: Tywin's brother and right hand man, has a more prominent role in the books.
Edric Storm: A young boy who is King Robert's most well known bastard son since his mother is a noble lady.
Vargo Hoat: Leader of the mercenary company The Brave Companions who currently operate in the Riverlands. He hath a very pronounthed
Ser Dontos Hollard: Appears briefly in the TV show, but has a much more expanded role in the books. After he is demoted to jester, he starts secretly helping Sansa after she saved his life. He is currently planning Sansa's escape.
Qyburn: He is still a disgraced former Maester, but in the books he is part of The Brave Companions mercenary group.
Q. What story changes do I need to know to start reading?
Here's a quick breakdown by story line:
The Starks at Winterfell:
* The Stark children are much younger. At the beginning of the story Robb and Jon are 14, Sansa is 11, Arya is 9, Bran is 6, Rickon is 3.
However GRRM has expressed that if he had to do it all over again he
would age up the children.
* There are plenty of rumors going around about the identity of Jon's mother. Chief among them is that the mother is Lady Ashara Dayne,
sister of Ser Arthur Dayne a knight of the Kingsguard that Ned
defeated in combat with the help of his friend Howland Reed during the
rebellion. Ashara committed suicide soon after.
The Starks in King's Landing:
* A recurring flashback that Ned has is the famous Tower of Joy scene. Back during the final days of the rebellion, Ned Stark and six
companions arrive at the Tower of Joy where Lyanna Stark is being
held. They are met by three Kingsguard knights. Details after that are
blurry. We know that all three Kingsguard were killed, but not before
grievously wounding Ned and killing all his companions except for
Howland Reed. Lyanna dies as well in a "bed of red" extracting a
mysterious "promise" from Ned before dying.
The War with Robb Stark:
* Tyrion didn't sleep through the Battle of the Greenfork, and he played an active combat role.
* Tywin never takes command of Harrenhall, and thus he never met Arya. Harrenhall is commanded by Gregor Clegane, then afterwards by his
underling Ser Amory Lorch who is aided by the mercenary company The
* Arya uses her final kill to free the Stark affiliated prisoners. That action along with The Brave Companions betraying the Lannisters,
and the timely arrival of Roose Bolton changes the ownership of the
castle to Roose Bolton. Jaqen then leaves. Arya continues to hide
her identity and serves as Bolton's page. When Bolton decides to leave
and join the war effort, he leaves The Brave Companions in charge, and
abandons Arya. It is then that Arya stages her escape with Gendry and
Hotpie, and kills the guards herself.
* In the books there is no Locke. His role is mostly taken up by Vargo Hoat who at the time was serving Roose Bolton.
* Robb attacks and defeats House Westerling, a vassal of House Lannister. Robb is heavily wounded and is treated by Jeyne Westerling.
When he receives the (false) news of the death of Bran and Rickon he
is devastated and seeks comfort with Jeyene. To restore her honor (and
because he fell in love with her) Robb marries Jeyne, and House
Westerling swears fealty to Robb Stark. Jeyne never got pregnant with
Robb's child (as far as we know), and she (and her family) were not in
the Twins when the Red Wedding occurred. She is still alive with her
The War with Renly Baratheon:
* House Florent (King Stannis's in-laws) side with Renly, and only change sides to Stannis when Renly is killed by the Shadow Baby.
The War with Stannis Baratheon:
* Ser Davos doesn't start as the Hand of the King. He gets that promotion after he survives the battle of the Black Water.
* The seat of House Baratheon, Storm's End, continues to stay loyal to Renly even after his death. And refuses to release either the castle
or Edric Storm to Stannis. Melisandre releases a second Shadow Baby to
kill the castellan. Storm's End then falls to Stannis, and Edric is
captured. It is he (not Gendry) that Mel plans to sacrifice.
Lannisters and Company in King's Landing:
* While Lord Varys does tell the story of the sorcerer who cut him to Tyrion, he never captures him.
* Sansa is not promised to Loras Tyrell, but to his eldest brother Wylas Tyrell.
* Cersie is not engaged to Loras Tyrell either, but her father does plan to marry her off to Oberyn Martell.
* Tyrion's face wounds are much more severe, and he loses a large part of his nose.
* Bronn, for the most part, abandons Tyrion after he gets a knighthood for his role in the Battle of Blackwater. Tyrion's mountain clansmen
are also evicted from King's Landing after the battle.
* Sansa is much less friendly to Tyrion. During their wedding she refused to kneel so that Tyrion could put his cloak on her.
* When Theon captures Winterfell he releases a prisoner named Reek, who slowly becomes his right hand man (taking up the role of TV
* Ser Rodrik Cassel is not captured by Theon. He raises a small army to retake Winterfell. As he lay siege to Winterfell, Reek promises
Theon that he could bring help if he would release him. Theon does.
Just as Ser Rodrik is about to attack, a force of Bolton men arrive to
join him. But the leader of the Bolton war party betrays Rodrik and
kills him and the rest of his men. The leader turns out to be Reek
who reveals himself to be Ramsay Snow. Ramsay had taken the identiy
of his servant Reek to avoid capture for his many crimes. Ramsay then
betrays Theon, and kills his men. Winterfell is then torched, and it's
Bran and the Reeds:
* Jojen and Meera Reed arrive in Winterfell much earlier. They are sent by their father Howland Reed to serve Winterfell.
* Bran and Rickon part way much earlier. They are split up as soon as they emerge from the sack of Winterfell.
* The Reeds tell a story to Bran called the Knight of the Laughing Tree that hints (among other things) that Ned Stark shared a mutual
attraction with Lady Asahra Dayne (a long time before he married
Arya and the Brotherhood Without Banners:
* Melisandere never visited the Brotherhood, and as such never met Arya and Gendry was never given up to her.
* Gendry "friend zoning" Arya never happens. In fact, we never get explicit confirmation that there's any attraction between the two.
* Among the Brotherhood is a former Stark guard who has converted to the Red God whom Arya briefly bonds with.
* Also among the brotherhood is Lord Dondarrion's squire Edric Dayne (also called Ned). Edric claims that Jon Snow's mother is a maid name
Wylla who was also his milk nurse.
The Night's Watch:
* Sam is never abandoned by Gren and Dolorous Edd, and he never witnesses the invading forces of the White Walkers the way it happens
in the TV show. He is, however, in camp at the Fist of the First Men
when the White Walkers and their Wights attack.
* It is during the aftermath of that battle that Sam encounters and kills a White Walker with the obsidian blade. This is witnessed by
many of his brothers and they start calling him Sam the Slayer.
* While Mormont is dying, he requests that Sam contact his son Jorah and ask him to join the Black.
* Orell dies when Jon ambushes Ygritte's group. His mind is trapped inside his eagle that attacks Jon much earlier than in the TV show.
* Ghost accompanies Jon when he is with the Wildlings.
* Tormund Giantsbane doesn't accompany Jon on his climb over the Wall. Instead the raiding party is lead by Styr the Magnar of Thenn.
Daenerys in Essos:
* At the beginning of the story, Dany is 13.
* Dany's first love making with Drogo is consensual and much more tender.
* Doreah doesn't betray Dany, but instead dies of heat exhaustion after Dany is abandoned by the bulk of her Khalassar.
* Dany's other handmaidens Irri and Jhiqui are still alive and gossiping.
* Dany's bloodriders are also still alive and continue to guard the Khaleesi.
* In Qarth, Xaro doesn't betray Dany to the Warlocks (though he doesn't help her either). Dany goes to the Warlock on her own (they
never kidnapped her dragons). After she destroys the House of the
Undying, the Qartheen decide to expel her from the city. It is then
that Arstan (the disguised Ser Barristan) and Strong Belwas arrive
with a gift of ships for Magister Illyrio. The ships are supposed to
take her back to Tyrosh, but she redirects them to Slaver's Bay.
* Yunkai is never sacked in the books. They surrender their slaves as soon as they realize that the mercenary companies they hired had gone
over to Dany.