Question about High Ground

I always here that high ground is everything, but I struggle to implement it. High ground is great for being able to a lot of your team and the enemy tank, but I often get forced off it because although I can see a lot, the enemy team can see me too and I get poked out. At that point, I'm often stuck out of position. I'm well aware Ana isn't a sniper although she seems to be, but there has gotta be a better way to get anti-nades besides lobbing them from the backline 20 meters away. Any advice on when high ground is a good idea?