Read John 3:7, 1 Corinthians 6:9-11, Matthew 21:31, 2 Peter 1:3-11
The first and most important qualification is to be born again. That is essential even to see the kingdom of God. It's not enough to be upright morally, diligent in good works, studying God's word or even praying. The Pharisee did all these things but they disqualified themselves by their self righteousness.
Paul explained who was disqualified from entering the Kingdom God. That's the negative. As an aside, a lot of believers use 1 Corinthians 6:9 to beat up on homosexuals. I've done that myself. However, I saw that it was just one of a list of sinful behaviours unacceptable to God. And verse 11 gives the answer: some of the Corinthians were that kind of sinner, but they found deliverance in Christ. No one is so deep into sin that he cannot be set free.
The key to entering the Kingdom is obedience to God's revealed will in this life. As I've said before, entrance into the kingdom of God is not the same as entering heaven. Those who are born again have eternal life. God will accept them as His own. But there will be no rewards for those who choose to live for themselves, avoiding the cross and being independent of God.
Lord Jesus said this to the Pharisees (Matthew 21:31). It helps to read the verses around verse 31 also.