I really enjoy reading Michael Gorman’s Reading Revelation Responsibly (Eugene: Cascade, 2011). For students of the New Testament, Revelation may be daunting. One of the reasons is that Revelation is an apocalyptic literature (as well as a letter and prophecy). The following description of apocalyptic literature by Gorman can be of great help.
Apocalyptic literature gives expression to apocalyptic theology. At the core of this kind of theology is a cosmic dualism, the belief that there are two opposing forces at work in the universe, one for evil (usually Satan and his demons) and one for good (usually God and the angels). This cosmic dualism gets embodied in real-life struggles between good and evil on earth, resulting in a more historical dualism of conflict between the children of God or light and the children of Satan or darkness. The reality of this cosmic and historical struggle means that every human must choose sides; one is historical struggle means that every human must choose sides; one is either on the side of good and God or of evil and Satan. We might label this ethical dualism. (p 15–16)
Apocalyptic theology includes another kind of dualism, a temporal dualism. It divides history into two ages, this age and the age to come. This present age is characterized by evil, injustice, oppression, and persecution, while the coming age will be a time of goodness, justice, and peace. Since these two ages are so antithetical, and since the current age is so completely infested with the power of Satan and evil, apocalyptic theology is marked by pessimism; there is no hope for a human solution to the crisis of this age. Only God can—and will!—intervene to set things right. Therefore, apocalyptic pessimism does not have the final word; it gives way to optimism. (p. 16)
Gorman also has some helpful words to say about Revelation itself (not apocalyptic literature in general). I will highlight a few things in blue.
Some scholars have compared the images in Revelation to political cartoons, full of symbolism, exaggeration, and fantasy. They are in vivid HD, 3D, big-screen color. Apocalyptic “employs a science-fiction-like idiom to describe events that exceed human capacities of expression.”  The vision “expands his [John’s] readers’ world, both spatially (into heaven) and temporally (into the eschatological future),… open[ing] their world to divine transcendence.”  (p. 19–20)
This all works together, almost like a sustained single vision, to express deeply held convictions about God and the world-stage on which the forces of good and of evil are at odds with each other. Thus apocalyptic theology and literature are inherently theopolitical in nature,… In Revelation, the cosmic struggle of God and the Lamb versus Satan (the dragon of ch. 12) manifests itself in the earthly struggle between God’s people redeemed by the Lamb and Satan’s agents, the beasts from the sea and the land—probably meant to signify the emperor and those who promote his cult. (p. 20)
Symbolic language is evocative and expressive; it is not the language of the newspaper but the language of poetry. Yet this symbolism points to actual, though transcendent, reality, so the language can be called “literal non-literalism.” “[T]he world created by symbols is not fictive; it is a non-literal real world.”  ”Furthermore, the “special genius of apocalyptic” literature, according to David Aune, is “its ability to universalize the harsh realities of particular historical situations by transposing them into a new key using archaic symbols of conflict and victory, suffering and vindication. Thus the beast form the sea [on Rev. 13] represents Rome—yet more than Rome.”  (p. 20)
Sources that Gorman cites above:
 George Beasley-Murray. The Book of Revelation (Grand Rapids: Eerdmans, 1974), 16–17.
 Richard Bauckham, The Theology of the Book of Revelation (Cambridge: CUP, 1993), 7.
 Wall. Revelation (Peabody: Hendrickson, 1991) 16.
 David Aune, “Revelation.” in The HarperCollins Bible Commentary. Edited by J. L. Mays. (San Francisco: HarperSanFrancisco, 2000), 1188.