Chapter 5 of the book of Galatians offers a stark contrast between the works of the flesh and the fruit of the human spirit (heart). Verses 19-21 list numerous works (sins) of the flesh, while verses 22 and 23 give us the nine fruits of the spirit, beginning with love. Most Christians-perhaps most people-will agree that we all can grow in love. I know I can, without having to ask the opinion of my wife, children, or others. Growing in the love of God is an ongoing process with everyone I know. Those who think that they've "arrived" are probably the ones needing to grow the most.
So, as far as growing, love, yes-but joy? How does a Christian grow in joy? How can one grow in joy, without getting goofy and weird? I mean, who wants to be one of "them?"
A Christian grows in joy just like one grows in love. How? By hearing verses about love, believing them in your heart, and acting like they're true in your own life. Remember, if you really believe God's Word in any area, you'll begin to act like it's true in your own life. If you don't than you may mentally agree with it in your head (mental assent), but not in your heart, where faith is.
Hearing verses and messages about the love of God will cause faith to come (Romans 10:17). Acting on God's love will cause fruit to grow in your life in the area of love. Over time, people will see that fruit exhibited in your life. Like telling an apple tree by the apples (fruit) on the branches, the fruit of love will show up in us, as spiritual branches.
The same is true about joy. The Bible has numerous verses about joy, in both the Old and New Testaments. Here are some of them:
Nehemiah 8:10; Psalm 30:5; Isaiah 55:12; John 16:24; Romans 14:17; James 1:2
As you keep hearing verses on joy, such as the ones above, faith for joy will come. Then, out of a believing heart, begin to act like you have joy. Not over night, but in time, as you continue to hear about God's joy, you'll become more joyful. Eventually, what's in your heart and mouth will affect your face. The fruit of joy will grow in your life even more.
Here's a link to a joyous service that will bless you in growing in the fruit of joy: https://www.youtube.com/watch?v=T7k45z3mAfY
It's a service in which people responded to what the Spirit of God was wanting to do: meet the needs of people as they responded to Him.