You should keep a good faction with the "Krrzck" as you can do several quests related to them. Not necessarily you can keep a good faction with "Z'zozicck Zhxizzckrrk", "The Watcher" and "The Tree of Ages" (treants/mantids) but this will almost keep going up automatically as almost any mobs will give you good faction on these. After being one time in Galladoria, they should be that friendly that you could commit genocide amongst them and they wouldn't mind.
You cannot raise your faction with these:
- Botonids
- Grazer
- Land Stalkers
- Minions of Balor (Tur Suil)
- Rotting Root
- Servitors of Myrddraxis (Fomor)
- The Tree Dervishes
But they are all aggressive so you don't have to worry about.
/edit: for the Krrzck faction, there is a pretty good spot to the very west of Necht for around level 36-42 if you want to get a good faction with them while leveling up.