Some of the Rifts in the Hinterlands are too high at the start of the game. You need to do the ones you can and come back to those later on when you have gained a few levels. Those were the only ones I recal having issues with but there might have been a handfull of others but I can't recal them so they must not have been an issue to me. But the few in the Hinterlands caused me problems until I realised I didnt need to finish every quest/mob in that zone at the beginning.
Go to the War table and open up a few zones. Do some quests/kills in them and gain a few levels before comming back to quests/mobs that were tough.
