I think listening to ATC + looking at your ND, or equivelant, might also be helpfull in avoiding collisons with other aircraft. It builds SA and helps to avoid TA's and RA's crucial if you have a limited view which you do from the flight deck of an airliner. But, yes, clearly looking out the window is important too, more important at low altitude if GA traffic is around, less important at FL390. Unfortunately the one that is going to hit you tends to be on a constant relative bearing so there is little or no relative movement which of course makes it tricky for the eye as does a low sun and a myriad of other things.
Its a desterate feeling in air combat when the other aircraft has tally on you but you can't see him/her.
Hit plenty of birds too, but still got hired, guess they only assumed I'd avoid other aircraft and mountains which so far I have, still failing on the bird front every now and then. Ho hum.