Choose a suitable magnification that would best suit your need.
Pick a larger objective lens if your main subject of focus is low-lit (e.g. stargazing).
A binoculars with a larger pupil diameter will offer a brighter view of your subject.
Lens performance directly affects the view you get. Pick one that gives you sharp and clear image without colour bias.
Picking a binoculars that could accompany you out in the elements.