Most people can relate to a football pitch (100m) reasonably accuratley, try doing this ie. 1 football pitch, 2 football pitches, more than one less than 2 etc....
Bracketing, for example, it's more than 150m but less than 250m, go for 200m then, if it looks less than half of that then 180m or the other way, more than half way, 220m
Another method is to train yourself. I take 108 steps to reach 100m on the flat, everyone will be different, I'm 5'8" with a 30" leg. Go to a football park and try it, 3 or 4 times normal strides, once you are happy, test your self, when out walking, look for a feature, have a good guess at it's distance then measure it using your pace method, will be reasonably accurate it will also get your eye and brain to read distances and be relatively confident at it.
I do sometimes get it wrong on new ground, but with getting to know the ground, it's features you should get reasonably good at it in a short period of time.
TJ