English - Go back x Come back

To go back means to return home, to a place (your house, your apartment, your country, your city, etc.), to where you were before (away from speaker).

Go back implies that the speaker is currently not in the place being talked about. "In February, I plan to go back to China" means right now I am not in China, but I have been there before and I plan to return in February.

So, my friends in China might ask, "When do you plan to come back?"

I could respond, "I plan to go back in February."

Other examples:

-      We had a great holiday in Spain last year. We are going back this year.

-      I had forgotten my passport and had to go back to get it.

To come back means to go somewhere else, and then return to the same place where they were, to go to a different place (anywhere, it doesn’t have to be home), to return to a place one has been before, here (where speaker resides).

Come back implies that someone is going to return someplace they have been before. If in a conversation, it is to the place where the person is currently located. Example: "When will you come back home?" (The person asking the question is at home). "Next week."

Or, "I had a great time in San Francisco. I hope I will be able to come back next year." (The speaker is in San Francisco, but will have to leave. He wants to return later). 

Other examples:

-      Max left our office, but quickly came back after discovering he had left his keys here.

-      Come back to London soon, I will miss you while you are away.

Source: Longman Dictionary, Google – Phrasal verbs