I am not sure how familiar you are with the rules but I'll try to help. If anything doesn't make sense ask!
I echo Frerin's statements about trolls and ringwraiths. I would like to note that the named ringwraiths quite useful in filling specific roles and if you can put any ringwraith on a mount (even a horse) it lets you bring his powers to bear more easily.
If you want shooting I would advise orc trackers because they give you 4+ shooting and are only 5 points each.
I'm not sure how many points you mean by small, but I find it tough to keep up my numbers with morannon orcs at smaller points matches. I find it tough to afford an extra 2-3 points per model when trying to squeeze in an expensive unit sometimes. (It's a judgement call IMO)
You have lots of 3 might heros such as Gorbag and Grishnakh available for relatively cheap.
Don't overlook Barad Dur Black Guard (especially the captain) or Morgul Knights/Warg Riders. They can each fill specific roles for your force.
The best thing about Mordor is that you can build an army to nearly any play style you like! In my opinion they have the most versatile unit list of any faction. Find a style and tactics that fit you and build an army that plays into those well. This will help sound tactical decisions come more naturally to you!
This is Mordor cut loose and have fun with it!