I had trouble getting it too for a while. There always seemed to be too much activity. Try at different times of day and approaching the area from different directions.
It gets better once you get used to it. I did a ton of wrong things like you early on. Just take you time, explore and don't rush through the missions. Things get much easier with better stats and equipment.
If you are talking about the final Bronte mission, I had a glitch in that one where an enemy in the house became invincible. We couldn't kill him and he couldn't kill us.
I reloaded a previous save and it worked fine after that.