**Repute**  
We know that any knight can make a knight<sup>**1**</sup>, but to make it '**stick**' the knighting knight needs to have the appropriate renown, as explained by the greatest knight of all, [Ser Barristan "The Bold" Selmy][1]:

<sup>[*A Dance With Dragons*:]</sup>
>! As he watched them at their drills, Ser Barristan pondered raising Tumco and Larraq to knighthood then and there, and mayhaps the Red Lamb too. It required a knight to make a knight, and if something should go awry tonight, dawn might find him dead or in a dungeon. Who would dub his squires then? On the other hand, **a young knight’s repute derived at least in part from the honor of the man who conferred knighthood on him**. It would do his lads no good at all if it was known that they were given their spurs by a traitor, and might well land them in the dungeon next to him. They deserve better, Ser Barristan decided. Better a long life as a squire than a short one as a soiled knight.<br /><sup>*-A Song of Ice and Fire: A Dance With Dragons, Part Two - After the Feast (The Kingbreaker).*</sup>

**Behaviour**  
A Knight is generally one who is chivalrous and upstanding<sup>**2**</sup> - barring the few who use the title as a means to a gains - this is what sets them apart from normal men (as well as the armor and weaponry.

**We ride spinners**  
A small point which I picked up is that people can almost tell someone is a knight from the horse they ride:

>“Salt pork never pleases me.” The pitchfork knight gave Clegane only the most cursory glance, and paid no attention at all to Arya, but he looked long and hard at Stranger. The stallion was no plow horse, that was plain at a glance. One of the squires almost wound up in the mud when the big black courser bit at his own mount. “How did you come by this beast?” the pitchfork knight demanded.<br />...<br />
“Because knights are fools, and it would have been beneath him to look twice at some poxy peasant.” He gave the horses a lick with the whip. “Keep your eyes down and your tone respectful and say ser a lot, and most knights will never see you. They pay more mind to horses than to smallfolk. He might have known Stranger if he’d ever seen me ride him.”
> <br /><sup>*-A Song of Ice and Fire: A Storm of Swords (Arya).*</sup>

<hr />
<sup>
**1.** From *A Dance With Dragons*:

> “Ser Rolly,” said the big man. “Rolly Duckfield. **Any knight can make a knight, and Griff made me**. And you, dwarf?”<br />*-A Song of Ice and Fire: A Dance With Dragons, Part Two - After the Feast (Tyrion).*
</sup>

<sup>**2.** From the [wiki][2]:
> Knights are supposed to be brave, courageous, honorable, and true to their word. They should be loyal to their feudal overlord, and are tasked with defending their faith. In practice, most knights fall short of sustaining such high and noble ideals. Many do not try particularly hard, and instead seek knighthood mainly for the prestige and opportunities.


  [1]: http://awoiaf.westeros.org/index.php/Barristan_Selmy
  [2]: http://awoiaf.westeros.org/index.php/Knight