ポイント1: 話す人からの視点 (Speaker's point of view)
Japanese uses different expressions according to the speaker's position relative to an action or event.
Movement toward the speaker's position or time: 来る / ~てくる
Movement away from the speaker's position or time: 行く / ~ていく
ポイント2: Common cases (Part 1)
Use ~てくる when an action is performed before coming or returning toward the speaker; use ~ていく when an action is performed before going away from the speaker.
ポイント2: Common cases (Part 2)
~てくる describes movement toward the speaker's location; ~ていく describes movement away from the speaker's location.
ポイント2: Common cases (Part 3)
Use ~てくる when information, an object, a smell, a sound, or an event reaches or enters the speaker's perception.
ポイント2: Common cases (Part 4)
~てくる describes a change or continuing state from the past up to the present; ~ていく describes a change or state continuing from the present into the future.