John 4:23-24 (KJV) says:
But the hour cometh, and now is, when the true worshippers shall worship the Father in spirit and in truth: for the Father seeketh such to worship him. God is a Spirit: and they that worship him must worship him in spirit and in truth.
The word worship here means to kiss, like a dog licking his master's hand; to fawn or crouch to, to prostrate oneself in homage, to do reverence to, to adore.
True worship gets close enough to God's face that you can kiss Him with the worship from your heart. You bow low. You humble yourself to lift God up. You exalt God for who He is: your heavenly Father.
In spirit refers to to worshipping God from your heart, and not just with your intellect or your emotions. Your heart, or your spirit man, is in your worship.
In truth means that your life is lived according to God's Word. Because God's Word is truth, you don;t tell God that you love Him and live a life of sin. Your heart of worship matches a life of truth.
Now is the time to worship your heavenly Father. God's eyes look for a person whose heart is in His worship and his heart is on his God. Nothing or no one should be before God. When you love God with all your being, your worship will reflect it. True worship is when your heart is loving God, your mind is stayed on God, and your body is used as an instrument of obedience and service to God. When all we do is done because we love God, it is expressed in our worship to our heavenly Father.