Equip the Iron Banner emblem and shader as soon as you reach Rank 1 : DestinyTheGame

It will increase your Iron Banner rep earnings by 20%

An Iron Banner Crucible win with both the shader and emblem equipped, will net you 30 rep (up from 25 without), you can also wear a faction class item and earn rep for that faction at the same time.

When you reach rank 2, equipping the Iron Banner class item will boost your rep gains by another 10%