And he said unto him, Why call you me good?     there is none good but one, that is, The Lord: but if you will enter into life, keep the commandments. Mat 19:17 Jesus' question was to see if the man recognized Him as the Lord in the flesh.

So, we see that only God is Good.   

What is a Christian?   

And when he had found him, he brought him unto Antioch.     And it came to pass, that a whole year they assembled themselves with the church, and taught much people.     And the disciples were called Christians first in Antioch. Act 11:26

So, we see that a Disciple is a Christian.   

Putting Good and Christian together, a Good Christian is a Spirit Filled, Follower of Jesus Christ.   

Jesus often emphasized the difference between a Believer and a Disciple as follows:

But that on the good ground are they, which in an honest and good heart, having heard the word, keep it, and bring forth fruit with patience. Luk 8:15 hearing, keeping and doing the Word.

But he said, Yes rather, blessed are they that hear the word of the Lord, and keep it. Luk 11:28 physical blessings are no comparison to spiritual blessings which are receieved by hearing, believing and keeping the Word Of The Lord.

Jesus answered and said unto him, If a man love me, he will keep my words: and my Father will love him, and will come unto him, and abide in him. Joh 14:23 Having a Love Of The Truth (with Christ being the sum of all Truth) is necessary for us to be obedient and therefore experience the manifestation of the Father's love in and through us.

He that loves me not keeps not my sayings: and the word which you hear is not mine, but the Father's which sent me. Joh 14:24 Jesus is very pointed about love.     It demands obedience.     This is not the obedience of legalism.     It is the obedience of faith in the Truth which is effected in us supernaturally.      Being In Christ causes us to understand that Jesus is the image of the Holy Spirit who is the Father.

It is clear from the above that Keeping the Words of Christ identifies a person as a Disciple, a Follower, a Good Christian.   
In the passage below Jesus tells us what His Expectation is for us.   

Truly, truly, I say unto you, He that believes on me, the works that I do shall he do also; and greater works than these shall he do; because I go unto my Father. Joh 14:12 This is one of the most ignored things that Jesus said.     Why?     Because we choose to be believers only.     We resist becoming disciples.      Disciples follow their master in His footsteps learning from Him and imitating Him.      Jesus is telling us that we are to spread the Gospel, heal the sick, set captives free and make disciples of all men.      We can only do this by the power of the Holy Spirit operating in a vessel with the Mind Of Christ.      What did Jesus mean by 'I go unto my Father'?     Jesus returned to the Spirit Realm ( Heaven) when He ascended where the Holy Spirit Father is most readily experienced.     It is the seat from where The Majesty emanates throughout the universe.

Hence, a Good Christian is not just a Believer but a Follower, a Disciple, as well.   
Good Christians emulate their Master, Jesus.   

The Foundation of our Faith is the Word, both the Incarnate Word and the Written Word.   We cannot be shallow, half-hearted, or reserved about our Faith and be Good Christians - at least not in the Master's eyes.   

Get into the Word and Pray in the Holy Spirit so that at His appearing you are found to be a Faithful and Wise Steward.   

Who then is a faithful and wise servant, whom his lord has made ruler over his household, to give them meat in due season? Mat 24:45 We are faithful and wise in Christ's eyes when we are doing His will.     His will is for us to be witnesses of Him in every aspect of our lives.      The Meat that Jesus refers to is the Gospel of the kingdom.