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: 
This may seem kind of obvious, but I use a scanning technique. I like to look at the next 10-20 feet, look up on all sides, look down, and then look up. It's a lot like driving, scan your mirrors, then your environment, then your dash or whatever you need to, and then repeat. It does take mental purpose, so you will have to train yourself. 

I like to scan ahead, look up at one area, say my right, scan, and then look to the left. Mostly it is second nature.
I hike with my feet slightly turned upwards against the direction they are moving. This prevents stubbing or anything abrupt and lets me get a firm grip on the firmament whether I see it or not. Also, after some thought, I tend to place my foot from the back-outside to front-inside and let it settle a bit until I feel it catch and then apply weight; for places with loose or jagged terrain, or simply where I want to move with the ground that is really helpful for me.

Personally rather than scan, I sort of observe, which lets me see beneath and above, then too I listen since a lot of snakes I can hear or catch their motion visually. 

To me the ground really isn't overly concerning, if I can see the challenges in general, and don't have to be concerned with the nitty-gritty of minor debris than I am golden.