1. Explain it simply
Put the direction complement 来 or 去 straight after a motion verb: 回来, 进去.
来 means toward the speaker; 去 means away from the speaker.
The word order is verb + 来/去, never 来/去 + verb.
Put 了 after the complement: 他回来了, not 他回了来.
2. Show examples
他回来了。
Tā huílái le.
He came back.
来 = toward the speaker
弟弟上去了。
Dìdi shàngqù le.
My younger brother went up.
去 = away from the speaker
请你进来。
Qǐng nǐ jìnlái.
Please come in.
imperative, no 了
3. Share a tip
Choose 来 or 去 by where the speaker stands, and keep the complement right after the verb - say 回来, not 来回.

