In my understanding; the Gospel of John has an uniquely important position in all of Christian Scripture, and indeed in all the world's writings - because of its author. The author was the disciple whom Jesus most loved, an eyewitness of his ministry; and the events of his death and resurrection.
The author of the Gospel was also, I believe, Lazarus - the first Man to be resurrected to immortality and re-named John - still alive and active in the world, until the second coming. He was sister to Mary of Bethany; who anointed Jesus's feet in a ceremony of sacred marriage after which she became Mary Magdalene and was the first to discover and speak with her resurrected Lord. Mary Magdalene and John were present with Jesus's mother Mary at Jesus's crucifixion; when John was given care of Jesus's mother.
All of this makes John's Gospel potentially of primary value for Christians - the 'source' above all others; the first source in importance, which should structure our interpretation of all other sources.
When I read the Gospel, in a proper state of mind that is both attentive and also open to its deep meanings, I find that it is - unlike the other Gospels, which read as reverend miscellanies and comprehensive compendia of memoirs - a through-composed, thematic and structured piece of writing in which everything written is of importance.
Furthermore, John's Gospel is almost wholly symbolic in its language and implications - it is absolutely not supposed to be read as a prose account of Jesus's life; but as a mystical, deep, poetic text from those who already know the basics and necessities, and have an ability to feel the resonances and implications.
This much is clear from many, many passages and parables in which Jesus's words are quoted both to demonstrate and to explain that this is what is going-on in the Gospel - again and again Jesus is asked for a straight, factual explanation of something and replies with a figurative one.
This is why I can only read and comprehend John's Gospel when I in a similar state of mind - when I am at a level of consciousness such that the symbolic, figurative, and poetical are natural and spontaneous modes of expression.
This is not a Gospel to decode or dissect or examine under a high-powered textual microscope; any more than is a soliloquy of Hamlet or a lyric by William Blake. John's Gospel is not a code - any more than Coleridge's Xanadu is a code! That attitude is guaranteed to miss the point and close-off even the slightest possibility of responsive and valid understanding.
Therefore, there can be no recipe for reading John's Gospel, no Footnotes or Cliff Notes encapsulation, no prose summary capturing what it 'means' - and the only advice I can offer is: to read it when you, personally, are at your best and most elevated; and then read it in solitude and with concentrated and trance-like attention.
Then, and only then, may it speak to you.
Note: Commenter WmJas points out that the author of the Gospel of John may NOT have been named John - the author of the Gospel may NOT be John the son of Zebedee named in the other Gosepls. The author of John's Gospel names himself as the disciple whom Jesus loved, ie. the Beloved Disciple. So my contention should be rephrased that Lazarus was resurrected as the Beloved Disciple, author of the text called the Gospel of John.