How to identify a false prophet

How can a Christian identify a false prophet or teacher?  What are the signs that we can look to for proof of false teachings?  What Bible verses can help us to identify wolves in sheep's clothing?
Warnings about False Teachers and Prophets

The New Testament is full of Scriptures warning Christians about false teachers and false prophets.  Jesus Himself said that "false messiahs and false prophets will appear and perform great signs and wonders to deceive, if possible, even the elect" (Matthew 24:24).  Peter warned that "there were also false prophets among the people, just as there will be false teachers among you. They will secretly introduce destructive heresies, even denying the sovereign Lord who bought them bringing swift destruction on themselves" (2 Peter 2:1). Sadly, "Many will follow their depraved conduct and will bring the way of truth into disrepute. In their greed these teachers will exploit you with fabricated stories. Their condemnation has long been hanging over them, and their destruction has not been sleeping" (2 Peter 2:2-3).  Paul reiterated "prophets should speak" but that "the others should weigh carefully what is said"  because time will tell whether what they say is true or not (2 Corinthians 14:29).
Is There Another Gospel?

Paul says that there is another gospel out there but any other gospel than the one that Paul or the other apostles taught is not from God but from His opposite - the Devil.  Paul was "an apostle sent not from men nor by a man, but by Jesus Christ and God the Father" (Galatians 1:1) and so we know that Paul taught the true gospel.  He wrote that "I am astonished that you are so quickly deserting the one who called you to live in the grace of Christ and are turning to a different gospel - which is really no gospel at all. Evidently some people are throwing you into confusion and are trying to pervert the gospel of Christ.   But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let them be under God's curse! As we have already said, so now I say again: If anybody is preaching to you a gospel other than what you accepted, let them be under God's curse" (Galatians 1:6-9).

Paul tells us that there is another gospel but, paradoxically, it's not really the gospel for the real gospel is the "good news."  The other gospel is bad news because it is based upon works and its author is the Devil.  If the gospel given to Paul (Galatians 1:1) was based upon works then we would all be in real trouble.  Paul says that the "gospel I preached is not of human origin.  I did not receive it from any man, nor was I taught it; rather, I received it by revelation from Jesus Christ" (Galatians 1:11-12) "for if someone comes to you and preaches a Jesus other than the Jesus we preached, or if you receive a different spirit from the Spirit you received, or a different gospel from the one you accepted, you put up with it easily enough" (2 Corinthians 11:4).  Paul says that they could receive a "different spirit" that differs from the Spirit.  The capitalized "Spirit" refers to the Holy Spirit and it is capitalized because it is a proper noun, a specific person in the form of God the Holy Spirit.  Conversely, if it is a "spirit" this is an evil spirit or wicked demon spirit and the source is from Satan.  That's why Paul was so surprised that they put up with it, or accepted it (2 Corinthians 4:11).
How to Identify False Prophets or Teachers

When people buy things they compare the original next to the imitation and that's how you can tell the false or imitation ones from the original.  U.S. Customs Authorities have confiscated millions and millions of imitations that had the original name brand on them but when they compared them to the original or authentic products, they could tell that the imports were phonies.  That is how you can compare false teacher's and prophet's teachings.  Hold their teachings against the originals that are contained within the Old and New Testament.  For example, when someone tries to tell you that you are commanded to abstain from what they call unclean meats, compare this teaching up against what Jesus said in Matthew 15:11 that "It is not what enters into the mouth that defiles the man but that which comes out of the mouth that defiles man" and what Paul wrote, "All food is clean, but it is wrong for a man to eat anything that causes someone else to stumble" (Romans 14:10) and that "everything God created is good, and nothing is to be rejected if it is received with thanksgiving" (1 Timothy 4:4).

You could also compare what some teachers or prophets say about salvation that you are required to do this or to do that and, in essence, teach that works are necessary for salvation.  Most believers understand that this isn't true because it is written that "it is by grace you have been saved, through faith—and this is not from yourselves, it is the gift of God —  not by works, so that no one can boast" (Ephesians 2:8-9).  That is a huge relief for Christians because if works were involved, we would always be wondering if we had done enough to earn our salvation and be saved.  The Thief on the Cross never had time to be baptized, never had a chance to attend church, and could not come down off the cross to do any good works.  It was all a matter of trusting in Christ to save him.  For example, if salvation was based on works or obedience, then the Thief on the Cross would have been doomed.   Thankfully we are not saved by works and this is why Jesus assured him that "Today, you will be with me in Paradise" (Luke 23:43).
Christians Don't Live in Sin

Another way to see whether you are hearing the true gospel or are being fed lies (with another gospel) would be to see if living in a certain lifestyle that is un-repented of does not matter to God.  I have heard some describe themselves as "carnal Christians" but this is an oxymoronic statement!  They might say that "I still sin but that's okay because I am saved by grace…and so it doesn't matter."  This is what is called licentiousness and it is a sin of presumption (Jude 4).  They see grace as a license to sin.  Nothing could be further from the truth.  The teaching that a person can be saved and yet live in sin is truly an error of epic proportion.  First John chapter 3 is clear about this saying that "No one who lives in him keeps on sinning. No one who continues to sin has either seen him or known him. Dear children, do not let anyone lead you astray. The one who does what is right is righteous, just as he is righteous" (1 John 3:6-7). John is crystal clear about this because he wrote that "No one who is born of God will continue to sin, because God's seed remains in them; they cannot go on sinning, because they have been born of God. This is how we know who the children of God are and who the children of the devil are: Anyone who does not do what is right is not God's child, nor is anyone who does not love their brother and sister" (1 John 3:9-10).  Here is evidence of those who we know are Christian and those we know likely are not.  They don't continue in sin and are the children of God but those who live in sin as a continual lifestyle are children of the Devil.  How easy that is to see.

Paul tells the church at Corinth, "do you not know that wrongdoers will not inherit the kingdom of God?  Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor men who have sex with men nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God" (1 Corinthians 6:9-10).  Some pastors or priests are not only living in sin as homosexuals, they even marry such couples despite the fact that Scripture condemns those who do.  "Anyone who…does not continue in the teaching of Christ does not have God" (2 John 1:9) and "If anyone comes to you and does not bring this teaching, do not take them into your house or welcome them. Anyone who welcomes them shares in their wicked work" (2 John 10-11).  Paul agrees that "If anyone teaches false doctrines and does not agree to the sound instruction of our Lord Jesus Christ and to godly teaching, the he is conceited and understands nothing" (1 Timothy 6:3-4a).
Conclusion

You can identify false teachers and false prophets by their teachings. If there is an uneasy feeling that it doesn't square up with Scripture, then study the Word to see if it either lines up with biblical doctrine or it doesn't (2 Timothy 2:15-16).  The best way to keep from being deceived by false teachers and prophets is to be a good Bible student yourself.  If you know the Scriptures well enough, you will be prepared to know what is error and what is not.  Reading the Bible daily is clearly one of the best methods for keeping one's self from believing false teachings or a false gospel…which is not really another gospel but is a gospel from the Devil.  And we are warned to not even entertain them in our house or in our minds.  What a great privilege it is because "you also were included in Christ when you heard the word of truth, the gospel of your salvation. Having believed, you were marked in him with a seal, the promised Holy Spirit" (Ephesians 1:13).