To follow the Holy Spirit from God, we need to be able to recognize the “voice” speaking to us as we make our daily, moment by moment choices. We cannot take for granted that any urge we might have or any teaching we might hear actually is God's leading. John, the last living apostle of the Twelve, felt compelled to warn the church Jesus promised to build:

Beloved, do not believe every spirit, but test the spirits to see whether they are from God, for many false prophets have gone out into the world.
1 John 4:1 ESV

In his next two sentences he gives the first test:

By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God, and every spirit that does not confess Jesus is not from God. This is the spirit of the antichrist, which you heard was coming and now is in the world already.
1 John 4:2-3 ESV

He tells us in verse 1 that false prophets/teachers speak from a spirit not from God. No human teacher gets it right all the time simply because no human has all the information God has, but teachers speaking by the Spirit of God can be recognized. God's word is reliable, but too often human interpretations don't take all factors into consideration in forming those interpretations. A misguided interpretation (or application) does not necessarily indicate the teacher is a false prophet, but we do need to be alert to test all teachings by the whole of Scripture, the surrounding context and historical context.

God's Spirit will lead his messengers to acknowledge that Jesus is God who became flesh. Notice that John tells us that the spirit of antichrist does not acknowledge Jesus as God come in the flesh and that spirit was in the world in his day as it is in ours.

The next test John addresses tells us the teachings of the biblical Apostles, whose teachings are in our Bibles, will be the source for true teaching. Those who deny those teachings are not from God. They are not speaking by God's Spirit, but by a different spirit.

They are from the world; therefore they speak from the world; and the world listens to them. We are from God. Whoever is not from God does not listen to us. By this we know the Spirit of truth and the spirit of error.
1 John 4:5-6 ESV

Who are the “we” and the “us” in this passage? Isn't it John and the other Apostles whose writings have been preserved for us today? Isn't he contrasting the teachings passed from Jesus to his disciples and then to the growing church with those of false teachers who contradict those teachings?

John reveals another test:

Anyone who does not love does not know God, because God is love.
1 John 4:8 ESV

John describes love as the kind of love God the Father and Jesus his Son showed toward us. If we, or teachers, are not showing that self-denying love, that teacher is not of God.

Some will teach that since we are saved by God's grace through faith that God's commandments are at best optional; but that is not what John or Jesus taught. We cannot be saved from sin and death by our “good works,” but we are saved to do good works among which are loving God and loving neighbor by not only avoiding the sins listed in The Ten Commandments, but going above and beyond to giving to others rather than stealing from them, as an example.

By this we know that we love the children of God, when we love God and obey his commandments. And his commandments are not burdensome.
1 John 5:2-3 ESV

The remaining test John writes returns full circle to the original test of who Jesus is:

Whoever believes in the Son of God has the testimony in himself. Whoever does not believe God has made him a liar, because he has not believed in the testimony that God has borne concerning his Son. And this is the testimony, that God gave us eternal life, and this life is in his Son. Whoever has the Son has life; whoever does not have the Son of God does not have life.
1 John 5:10-12 ESV

When God's Spirit in you seems to give you a warning something might be off in a teaching, look carefully at what is being taught and compare to the Scriptures which are “God-breathed” (1 Corinthians 14:29; Acts 17:11). Trust in the understanding God gives through his Spirit and his word (1 John 5:20-21).