If you can't do their quests, kill NPC:s from factions that they are mortal enemies with.

Make sure not to kill the civilians if the factions does not approve of war crimes

You need +50.0 Alignment with them to stop them from attacking you.

I'd suggest lurking around the Vales of Anduin near the Wood Elves Sphere of Influence and killing Gundabad Orcs or hunting Mirkwood Spiders.