False Doctrine is anything that is contrary to the word of God, I.E Denying the Deity of Christ, Insisting that works play a vital part on Salvation, insisting that there is no Hell, stating that you can lose your salvation, etc. basically teaching the opposite to the word of God.
The JWs do not rightly divide the word of truth, as they are not told how too.. yet, the Apostle Paul tells us that we are to do so, however this is oy something which the Holy Spirit can open our minds to do.
2 Timothy 2:15 KJV
Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.
2 Corinthians 4:4 KJV
In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.
1 Corinthians 2:12-14 KJV
Now we have received, not the spirit of the world, but the spirit which is of God; that we might know the things that are freely given to us of God.  Which things also we speak, not in the words which man's wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual.  But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned.
1 Corinthians 2:4 KJV
And my speech and my preaching was not with enticing words of man's wisdom, but in demonstration of the Spirit and of power:
1 Corinthians 2:13 KJV
Which things also we speak, not in the words which man's wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual.