Max out your Might points: Might wins games. I strongly suggest dropping all Banners; generally not worth the points. Mordor Uruks are not impressive...are you including them only because you have the models? If so, they need shields. Your Witch King needs a horse (or Fell Beast) for sight lines and manuverability, plus a Fate point or two if he is your leader (one lucky Elf arrow and he is dead). Orcs are squishy: low defense and fight. Black Numenorians with Orc Spears are your best bet, if possible (Defense 6, Fight 4 plus Terror). Trolls are good, but first to die, especially with no Might or Will. Maybe replace one Nazgul (the other two are plenty) with a Troll Chieften, instead. Consider:
Witch King Mounted 3M 12W 2F
6 BN
6 Orc Spear
Nazgul 2M 9W
6 BN
6 Orc Spear
Troll Chieften
6 BN
6 Orc Spear
At this points level, you will dominate; lots of magic, a hard to kill Monster with Might, and tough troops. Bows are nerfed to pointless in most Evil lists, and cavalry got suddenly fragile with Brutal Power Attacks. Get Lonely Knight's excellent SBG Armybuilder
http://lonelyknight.0fees.net/Hope this helps--and welcome!