I would single out three devices Wilde uses with particular skill: foreshadowing, irony, and symbolism.

The most obvious instance of the first of these is Dorian's wish that he will never age and that the portrait will age instead—of course, this is what ends up happening, except for one thing. In addition to "aging," the portrait also reveals Dorian's soul, his inner self and the "evil" he has become. This in itself leads to the second literary device, irony. It's ironic that Dorian, in making this wish, thinks the outcome will be something good for him. It turns out that the alteration of the portrait becomes a kind of self-perpetuating process. When Dorian notices that the picture has changed, after his first reprehensible act in rejecting Sibyl, this somehow causes him fatalistically to accept his descent and willfully to continue his downward spiral. And the portrait becomes more and more loathsome as he does so.

A second instance of irony, probably not often noted, is that Lord Henry, although a cynical man and a bad influence ultimately upon Dorian, is also a man who casually accepts the imperfections of the world, is amused by them, and even revels in them. Ironically it's precisely the opposite quality—perfectionism—that causes Dorian to blast Sibyl after her bad performance in Romeo and Juliet and then to cast her aside. It's doubly ironic that Dorian's desire for perfection in the world marks the start of the downward spiral of his life.

Another ironic element is that although we are never told precisely what Dorian is doing that makes him so "corrupt"—until the murder of Basil, at any rate—this corruption is the centerpiece of the story. The reader can assume many things, though the obvious ones mostly have to do with sex, both straight and gay. We are told that Dorian has caused women to be disgraced and also that he has a "fatal effect on young men." He and Alan Campbell had been the best of friends, absolutely inseparable. But then, we are told, something bad happened between them. When Dorian calls Campbell to the house to dispose of Basil's corpse, Campbell's attitude to him, even before being told about the grisly task, is hostile in a shameful, unforgiving way. Of course, in nineteenth-century English and American novels (unlike, for instance, French and Russian works of the same period), we are typically never given direct information about intimacy even between married men and women. So Wilde is not unusual in that respect, but the unique thing about The Picture of Dorian Gray is that something sexual forms the heart of the book, and it's therefore ironic that the reader must guess as to what exactly is happening. A less important point, incidental in itself, is that in his state of "corruption," we are told that Dorian "had a special passion, also, for ecclesiastical vestments, as indeed he had for everything connected with the service of the Church." It's possible that in the irony of this, Wilde is making an underhanded comment against religion, saying that the trappings of religion are attractive to "evil" people.

Wilde's use of symbolism can be seen in the choice of names for some of his characters. Sibyl Vane is not actually vain, but this is the way men view her, including her own brother James. When she appears on stage she's described in typically sexist language, as if she were a beautiful porcelain doll of some kind. The men, including Dorian, interpret her as being obsessed with her own looks to the exclusion of all else, though this is obviously not true.

Dorian's own name, Gray, is symbolic of an ambiguous middle ground between light and dark. He represents perfection and youthful innocence at first, and then corruption and evil later. As the story progresses, the dichotomy within Dorian—between his innocent appearance and his true self shown in the portrait—becomes worse and worse and is never resolved, for the two halves of Dorian are not brought back together but are in effect merely switched at the conclusion. The ugly portrait becomes the dead man, and the youthful, uncorrupted-looking man becomes the portrait again. This is the final irony, that in attempting to destroy the picture, Dorian destroys himself.

In The Picture of Dorian Gray, Wilde uses a number of literary techniques to develop his characters and to enhance some of the novel's key themes.

Allusions, for example, are widely used in Chapter One to reveal more about Dorian's appearance and character. He is likened to Adonis, a man of great beauty from Greek mythology, to demonstrate his visual appeal to the reader. He is also likened to Narcissus, another figure from Greek mythology, who fell in love with his own image and died because he could not stop looking at himself in the reflection of a pond. By including this allusion, Wilde also foreshadows Dorian's future and suggests that his self-love will develop into an unhealthy obsession.

Wilde also uses a number of symbols in the novel. The portrait, for example, becomes a living representation of Dorian's soul which degrades as his levels of vice and immorality increase.  It also represents the unavoidable process of ageing which Dorian is so keen to prevent. In addition, the yellow  book, given to Dorian by Lord Henry, is another important symbol because it demonstrates Lord Henry's corrupting influence on the young Dorian.

Witty sayings, called epigrams, are also an important feature of Dorian Gray. They not only enhance Wilde's lively writing style but also reveal much about the character of Lord Henry. He uses them, for example, to add a humorous element to his negative views on women:

Women are a decorative sex. They never have anything to say, but they say it charmingly.

That Dorian emulates Lord Henry's use of epigrams illustrates the extent of the latter's influence. One example comes from Chapter Four when Dorian speaks of Sybil Vane:

Ordinary women never appeal to one's imagination. They are limited to their century.

Furthermore, these epigrams are often ironic or paradoxical in nature:

There is only one thing in the world worse than being talked about, and that it not being talked about.

This use of irony suggests that Lord Henry and Dorian are superficial people; they are driven by a need to appear to be witty and intelligent. Dorian captures this idea in Chapter 19:

You would sacrifice anybody, Harry, for the sake of an epigram.

Unfortunately, Dorian's realisation comes too late: he cannot be redeemed from his life of vice and corruption as we see most clearly in his untimely demise.