Redditor Generic Dread Head has compiled a guide for the Iron Banner tournament in Destiny: The Taken King.
Information will be added to the guide overtime. Focusing on how to reach Rank 5 will all three characters, the guide says:
Lord Saladin is currently selling:
Drops traditionally begin at Rank 2 onwards and the rate of drops has increased so that they're now the primary source of rewards from the Iron Banner tournament.
The recommended mimimum light level for the Iron Banner is 230 and only a level 40 guardian can lead a fireteam. Gear can still be purchased from Lord Saladin but requires Legendary Marks rather than Glimmer.
Players begin at Rank 0, not Rank 1.
Standard Crucible bounties can now be completed during Iron Banner. Emblems, shaders, and class items from previous Iron Banner tournaments can be used, with their benefits being felt from the start. However, the class item has a very low light of just 30 and probably shouldn't be used.
Both Shader types (Rank 2 and 5) and Emblem types (Rank 1 and 3) will give you you the same Rep bonuses, while wearing Iron Banner Armour does not give any additional REP boost.
If you have no Iron Banner Emblem, Shader or Class Item, you'll need to add 20% to the amount of time/games required to level up.
There's plenty more in the guide.