A) 1-2:  The Divine WORD was with God eternally.
    B) 3:  All things came into being through it/him (the Word).
        C) 4-5:  In him was life and light, which darkness did not overcome.
            D) 6-8:  [John was not the light, but came to testify about the light.]
                E) 9-10:  The True Light was in the world, but the world did not recognize him.
                    F) 11:  He came into his own realm, but his own people did not accept him.
                        G) 12:  THOSE  WHO  DO  BELIEVE  IN  HIM  BECOME  CHILDREN  OF  GOD.
                    F') 13:  These believers are not ordinary human offspring, but are born of God.
                E') 14:  The Incarnate WORD reveals God's glory, full of grace and truth.
            D') 15:  [John testified about the priority of the one coming after him.]
        C') 16:  Out of his (the Word's) fullness, we all received grace upon grace.
    B') 17:  Grace and truth came into being through Jesus Christ.
A') 18:  The only-begotten Son has revealed God.

I) The Prophetic Testimony of John about Himself  (1:19-28)

  19a:  Literary Introduction: The testimony given by John [the Baptist].
19b:  Priests and Levites sent from Jerusalem question John: "Who are you?"
20-21:  John confesses that he is not the Christ, nor Elijah, nor the prophet.
22:  Searching for an answer: "Who are you? What do you say about yourself?"
23:  John answers, quoting Isaiah: "The voice crying in the wilderness; Make straight the way of the Lord."
24:  The ones sent by the Pharisees continue questioning John:
25:  Why does he baptize if he is not the Christ, nor Elijah, nor the prophet?
26-27:  Variation of answer: John baptizes with water, but is not worthy of the one coming after him.
  28:  Geographical Setting: John was baptizing in Bethany across the Jordan.

II) The Prophetic Testimony of John about Jesus  (1:29-34)

  29:  He [John] saw Jesus and declared: "HERE  IS  THE  LAMB  OF  GOD..." (cf. v. 35)
30:  After me comes one who ranks ahead of me, because he was before me.
31:  I myself did not know him, but came baptizing with water that he might be revealed.
32:  John testified: "I saw the Spirit descending from heaven like a dove, and it remained on him."
33a:  I myself did not know him, but the one who sent me to baptize with water said:
33b:  The one on whom the Spirit descends is the one who baptizes with the Holy Spirit.
  34:  I have seen and have testified: "THIS  IS  THE  SON  OF  GOD." (cf. v. 49)

A1) The First Two Disciples (1:35-39)
35-36:  John & two of his disciples saw Jesus: "Look, HERE  IS  THE  LAMB  OF  GOD." (cf. v. 29)
     37: The two disciples heard him [John] say this, and they followed Jesus.
38-39a:  Jesus sees the two following and dialogues with them:
     Jesus: "What are you looking for?"
     They: "RABBI, where are you staying?"
     Jesus: "Come and see."
39b: They came and saw, and remained with Jesus; it was about the tenth hour (4:00 p.m.).
 
A2) The Third Disciple (1:40-42)
40: One of the two disciples who heard John and followed Jesus was Andrew, brother of Simon Peter.
    41: He found his brother Simon: "We have found  THE  MESSIAH,  which is translated CHRIST."
        42: He brought Simon to Jesus, who says he will be called "Cephas," which is translated Peter.
 
B1) The Fourth Disciple (1:43-44)
43a:  Geographical transition: Jesus decided to go to Galilee.
    43b:  Jesus found Philip and said: "Follow me."
         44:  Geographical aside: Philip, Andrew, Peter were all from Bethsaida.
 
B2) The Fifth Disciple (1:45-51)
45-46:  Philip found Nathanael and dialogues with him:
     Philip: "We have found THE  ONE  ABOUT  WHOM  MOSES  AND  THE  PROPHETS  WROTE."
     Philip: "JESUS,  SON  OF  JOSEPH,  FROM  NAZARETH."
     Nathanael: "Can anything good come from Nazareth?"
     Philip:  "Come and see."
47-51: Jesus sees and dialogues with Nathanael:
     Jesus: "Here is truly an Israelite in whom there is no deceit."
     Nathanael: "How did you get to know me?"
     Jesus: "I saw you under the fig tree before Philip called you."
     Nathanael: "RABBI,  you are  THE  SON  OF  GOD (cf. v. 34);  you are  THE  KING  OF  ISRAEL."
     Jesus: "Do you believe because I told you I saw you?  You will see greater things."
     Jesus: "You will see heaven opened and God's angels ascending and descending upon  THE  SON  OF  MAN."
 

Note the dynamics of who calls whom to discipleship above:

#1&2 - John (the Baptist) sends two of his disciples to follow Jesus.
#1&2 - One is named Andrew, but the other remains anonymous.
#3 - Andrew brings his brother Simon (Peter) to Jesus.
#4 - Jesus finds and invites Philip personally.
#5 - Philip talks to Nathanael about Jesus.

Contrast: In Mark and Matthew, Jesus calls two pairs of brothers (Peter & Andrew, James & John) as his first disciples; while in Luke, the focus is mainly on Peter (for more details, see my page on Disciples and Discipleship).

Some scholars also highlight the temporal notices in this chapter:

1 - One day (implicit beginning in 1:19)
2 - "The next day..." (1:29)
3 - "The next day..." (1:35)
4 - Another day (begins 1:40, implied by late afternoon hour of 1:39)
5 - "The next day..." (1:43)
7 - "On the third day..." (2:1; the biblical way of saying "two days later")

Question: Did the evangelist really intend this as a sequence of 7 days?  If so, why didn't he explicitly say "The next day" in 1:40?  And how many days would it have taken to travel from "Bethany across the Jordan" (1:28) to "Galilee" (1:43) to "Cana in Galilee" (2:1)? (see the Geography of John's Gospel webpage).  Moreover, rather than merely completing a sequence of seven days, "On the third day" (2:1) serves to connect the story of the Wedding at Cana with the crucifixion and resurrection of Jesus (cf. 2:19-21; 20:1).