Question: Every time I go walking or hiking, I generally spend most of my time looking down to make sure I don't step on a snake or hole or dog poop. I don't do it consciously, it just happens. Obviously, I miss out on a lot of birds and small animals up in the trees and I'd like to see how other people cope with the urge to avoid obstacles and just enjoy their surroundings.

How can I go walking and hiking without constantly looking down?

Answer: 
I find this is something I do when I can't see much of the scene in front of me at once. This is normally because I'm not far from the person in front of me. Therefore, my advice is: walk in front. Or, leave a big gap between you and the person in front of you. This is perhaps somewhat antisocial, but personally I quite like to walk alone about half the time. It lets me focus on my surroundings a bit more.
Ha ha. You can't. At least not off a leveled surface. I've struggled with this too. If I look down I miss the views; if I look up I trip. So I look ahead for a place to stop and enjoy. Then I march on, eyes on the rocks and detritus in the trail, until I reach my looky place.