During visual flight conditions, when you see another aircraft in your path, you should strive to avoid hitting it.
In shipping there are standard international rules about which way boats should turn in order to avoid each other.
Are there similar rules in aviation?
well, you can tell which way it's pointing - even if you see a red light it could be moving left-to-right in your field of view (i.e. its bearing is increasing)
Sailors have a saying: Constant Bearing, Closing Distance means Collision!
Meaning: If another vessel is at a certain bearing (say, your 3 o'clock), and a certain distance, then several minutes later, it is still at your same bearing (3 o'clock again), but the distance is closer, then you will collide.
Instead, if the bearing changes, the traffic will pass in front or behind you. (if the bearing closes towards 12 o'clock, traffic will pass in front: If the bearing opens up towards 3 or 9 o'clock, traffic will pass behind)
It works great in relatively slow moving boats. it is a little harder to determine when planes are moving quickly, but the principle is the same: Is the bearing staying constant while the distance decreases? DANGER.
It's probably easier to miss traffic vertically than horizontally. The only problem there is you both make the same maneuver. There maybe should be some kind of rule of thumb that directly oncoming traffic on eastbound headings should climb and westbound should descend. And comverging traffic to the right climb and left descend.
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