In John 15, Jesus tells us that His disciples must bear fruit:
“I am the true vine, and my Father is the vine dresser. Every branch in me that does not bear fruit he takes away, and every branch that does bear fruit he prunes, that it may bear more fruit. Already you are clean because of the word that I have spoken to you. 
“Abide in me, and I in you. As the branch cannot bear fruit by itself, unless it abides in the vine, neither can you, unless you abide in me. I am the vine; you are the branches. Whoever abides in me and I in him, he it is that bears much fruit, for apart from me you can do nothing. 
“If anyone does not abide in me he is thrown away like a branch and withers; and the branches are gathered, thrown into the fire, and burned. If you abide in me, and my words abide in you, ask whatever you wish, and it will be done for you. 
By this my Father is glorified, that you bear much fruit and so prove to be my disciples.” (John 15:1-8, ESV)

If this issue of fruit production is so important, we must ask what kind of fruit is Jesus looking for? Clearly this fruit is the result of staying connected (abiding) to Christ. But what is the fruit that abiding in Christ produces?

To answer that question I looked at every occurrence of the word “fruit” in the Bible, and how it is used. I found the following 17 different uses of the word:

1. Literal Fruit
   (Gen 1:11-12, 29, 3:2-6, Gen 3:12, Ex. 10:15, Lev 19:23-25, 23:40, 26:4, 26:20, 27:30, Deu 20:6, Josh 24:13, Jdg 9:11, 2Sam 16:2, 2Ki 19:29, Neh 9:25, Ps 148:9, Ecc 2:5, Song 8:11, 8:12, Isa 32:10, Isa 37:30, Isa 65:21, Jer 31:5, Eze 25:4, Amo 9:14, Mic 7:1, Hab 3:17, Zec 8:12, Mat 21:19, 21:34, Mat 26:29, Mar 4:20, Mar 11:14, Mar 12:2, Mar 14:25, Luk 13:6,7, Luk 20:10, Luk 22:18, John 12:24, John 15:2, 1Co 9:7, Rev 6:13

2. Metaphor for Produce Generally
Gen 4:3, Lev 25:19, Num 13:20, Num 13:26, Num 13:27, Deu 1:25, Deu 7:13, Deu 11:17, Deu 26:2, Deu 26:10, Deu 28:4, Deu 28:11, Deu 28:18,
Deu 28:30, Deu 28:33, Deu 28:42, Deu 28:51, Deu 30:9, Deu 30:9, Jos 5:12, Neh 9:36,Ps 72:16, Ps 105:35), Isa 4:2, Jer 7:20, Hos 14:8, Joe 2:22, Jas 5:7), Jas 5:18, Rev 18:14)

3. Babies- Fruit of the Womb
Gen 30:2, Deu 7:13, Deu 28:4, Deu 28:11, Deu 28:18, Deu 28:53, Deu 30:9, Deu 30:9, Ps 127:3, Isa 13:18, Lam 2:20, Eze 36:8, Eze 36:30, Mic 6:7, Luke 1:42

It is easy to see that Jesus is not expecting His followers to be farmers and vine-dressers. Nor is He requiring us to have lots of babies.

4. Firstfruits
   This refers to the practice of offering part of the harvest, the first part gathered, back to the Lord in thanksgiving and in faith that He will protect the remainder of the harvest.
   (Exo 23:16) You shall keep the Feast of Harvest, of the firstfruits of your labour, of what you sow in the field. You shall keep the Feast of Ingathering at the end of the year, when you gather in from the field the fruit of your labour.

(Neh 10:35) We obligate ourselves to bring the firstfruits of our ground and the firstfruits of all fruit of every tree, year by year, to the house of the LORD;

(Neh 10:37) and to bring the first of our dough, and our contributions, the fruit of every tree, the wine and the oil, to the priests, to the chambers of the house of our God; and to bring to the Levites the tithes from our ground, for it is the Levites who collect the tithes in all our towns where we labour.

5. Fruit of the Heart
   (Deu 29:18) Beware lest there be among you a man or woman or clan or tribe whose heart is turning away today from the LORD our God to go and serve the gods of those nations. Beware lest there be among you a root bearing poisonous and bitter fruit,

(Jer 11:19) But I was like a gentle lamb led to the slaughter. I did not know it was against me they devised schemes, saying, “Let us destroy the tree with its fruit, let us cut him off from the land of the living, that his name be remembered no more.”

6. Metaphor for Strength and Vitality
   (2Ki 19:30) And the surviving remnant of the house of Judah shall again take root downward and bear fruit upward.

(Ps 1:3) He is like a tree planted by streams of water that yields its fruit in its season, and its leaf does not wither. In all that he does, he prospers.

Ps 80:12, Ps 92:14, Isa 27:6, Isa 37:31, Jer 11:16, Jer 12:2, Jer 17:8, Dan 4:12, 4:14, 4:21, Hos 9:10, 9:16, 10:1, Amo 2:9)

We could possibly see this as something that Jesus is expecting of His people. Abiding in Him produces the fruit of spiritual and emotional steadfastness.

7. Return From Work Or Effort
   (Ps 128:2) You shall eat the fruit of the labour of your hands; you shall be blessed, and it shall be well with you.

Job 20:18, Ps 78:46, Ps 104:13, Ps 105:44, Pro 27:18, Pro 31:16, 31:31, Eze 23:29

8. Return From Living A Sinful Life
   This would be the exact opposite of what the Lord requires.

(Pro 1:31) Therefore they shall eat the fruit of their way, and have their fill of their own devices.

(Hos 10:13)
You have ploughed iniquity; you have reaped injustice; you have eaten the fruit of lies.

Pro 14:14, Jer 6:19, Amo 8:1-2, Rom 6:21, Rom 7:5.

9. Wisdom or Righteousness
   (Pro 8:19) My fruit is better than gold, even fine gold, and my yield than choice silver.

(Mat 3:8) Bear fruit in keeping with repentance.

Pro 11:30, 12:12, Isa 3:10, Isa 11:1, Isa 27:9, Isa 45:8, Jer 17:10, Jer 21:14, Jer 32:19, Eze 34:27, Amo 6:12, Mic 7:13, Mat 3:10, Mat 7:17-19, Mat 12:33, Mat 13:23, Luk 3:9, Luk 6:43-44, Luk 8:14-15, John 4:36, John 15:4-8, 16, Rom 6:22, Rom 7:4, Gal 5:22, Eph 5:9, Php 1:11, Php 4:17, Col 1:10, Heb 12:11

10. Words- Fruit of the Lips
    I think Jesus is actually saying that He wants fruit that is in some way tangible, not just words, especially as the Old Testament prophets condemned Israel for honouring God with their words only.

Pro 12:14, Pro 13:2, Pro 18:20, Isa 57:19

11. Sexual Love
    This is only used in the Song of Songs, and in the context, this is not what Jesus is talking about.

(Son 2:3, Son 7:8)

12.A Snake
(Isa 14:29)
Rejoice not, O Philistia, all of you, that the rod that struck you is broken, for from the serpent’s root will come forth an adder, and its fruit will be a flying fiery serpent.

13. People
    Mainly used as an analogy by the Old Testament prophets, to refer to the people of Israel.

(Isa 17:6)
Gleanings will be left in it, as when an olive tree is beaten— two or three berries in the top of the highest bough, four or five on the branches of a fruit tree, declares the LORD God of Israel.

Eze 17:8-9,23 19:12-14

14. New heavens and earth blessing
    (Eze 47:12) And on the banks, on both sides of the river, there will grow all kinds of trees for food. Their leaves will not wither, nor their fruit fail, but they will bear fresh fruit every month, because the water for them flows from the sanctuary. Their fruit will be for food, and their leaves for healing.”

(Rev 22:2) through the middle of the street of the city; also, on either side of the river, the tree of life with its twelve kinds of fruit, yielding its fruit each month. The leaves of the tree were for the healing of the nations.

15. Sacrifices on the Altar
    (Mal 1:12) But you profane it when you say that the Lord’s table is polluted, and its fruit, that is, its food may be despised.
16. People being saved
    (Col 1:6) which has come to you, as indeed in the whole world it is bearing fruit and increasing—as it also does among you, since the day you heard it and understood the grace of God in truth,
17. Praise
    (Heb 13:15) Through him then let us continually offer up a sacrifice of praise to God, that is, the fruit of lips that acknowledge his name.

Conclusion
Some of these categories seem to be easily excluded. Looking at the context of John 15, it would seem that Jesus is saying that if we abide in Him, then outcomes such as a righteous life (9), or a sense of vitality and strength (6), people being saved (16) and praise from our lips( 17) should be expected.

In the end it is not about our efforts alone; after all a fruit tree does not strain to produce fruit. If we are true followers of Christ, then certain things will follow. We can often tell who the true christians are in a group or a community by observing the way they speak and act. This is the fruit of Christ within.