I was flying at around 30 metres, and you go need to know what is around you. I start normally with an overfly to scope out the surroundings and to get an idea for the shot I want
That way when you actually do the real shot, you know what your looking at and where your going. With the Mavic, the manual does give you some do's and don't 's, and stick to them, they are there for a reason. Don't rely on the VPS to keep you safe and out of the water, and know where you are.