The binoculars need to have a large objective diameter. Having a large objective diameter increases the field of sight. Putting it in other terms, the larger the diameter, the more light can get into your eye. With more light you will be able to see fainter objects. With binoculars with small objective diameters, you will not be able to get a lot of light into your eye, thus fainter objects will not be visible.

Get a pair of binoculars that has a magnification no greater than 7-8.
Also find a pair with a proper size exit pupil
Good eye relief is also important
Fully multi-coated optics
BAK-4 Porro prisms

Rugged design - Binoculars tend to be taken everywhere and tend to fall an extraordinary amount of time.
Having a rugged designed pair of binoculars will help to prolong the useful life of your binoculars.
Maybe a couple of other goodies

Company Resource: Big Porro Binoculars, Compact Porro Binoculars