Go to the undaunted stand in the factions main city to get your pledge quests, then either advertise yourself in zone chat or watch zone chat for people advertising they are looking for a (fill in your role here).

For EP, the undaunted quest givers are in Mornhold/Deshaan. For AD it's in Ghratwood, and I'm not sure where it is in DC land, I think Wayrest...but not sure on that.

So anyway, you just have to be in the right area, and watch zone chat and you will generally find a pick up group pretty easy.