Revelation 8:7 says all the grass was burned and Revelation 9:4 says they (those released from the abyss) were not to harm the grass. Was all the grass burned up, or not?
A "literal interpretation" is the exegetical method that enables the interpreter to understand the literal meaning of a given text. If, for example, you read the description of the "Lamb" in Revelation 5:6, you'll seek to understand the literal reality behind this obviously symbolic description. But to do this, you must consider the textual genre. The book of Revelation is made up of a series of visions, each of which is rich in symbolism, and it is clearly not of the same textual genre as, say, the book of Acts. If one doesn't recognize this, one will never be able to discern the literal meaning of any of Revelation's visions.
So I support the "literal interpretation" of biblical texts. But it's important to distinguish "literal interpretation" from interpreting literalistically. An example of the latter is when a person reads a highly poetic description like a newspaper report or historical account, and it simply doesn't work!
Here's an example:
Isaiah 14:4 states, "You will take up this taunt against the king of Babylon." Notice first that this is a "taunt" (a figurative parable, proverb, or poem), not a news report or historical account. Second, note that it concerns "the king of Babylon," who was the chief representative of an oppressive power. Then if you just read through the chapter, you'll see that it is highly poetic and loaded with symbolic language. We find trees—cypresses and the cedars of Lebanon—talking to one another about the absence of the king's axmen (verse 8). If we interpret literalistically, then we will conclude that trees are (or were) conscious entities and can (or could) communicate with each other. But suppose we seek to discover the literal meaning of the text. In that case, we'll recognize this particular textual genre for what it is and come to the understanding that this simply means that the king is no longer obtaining the finest wood to build his magnificent palaces—in other words, the king and his kingdom are coming to ruin.
If we consider the different kinds of texts we find in Scripture, then that will go a long way toward helping us understand what the various authors of Scripture were trying to convey to their audiences. Since Revelation is made up of visions containing highly symbolic descriptions, we should not read it as if it were giving us precise figures on how many, how long, or what percentage. We should not just automatically assume (or rule out) that all its references to "the earth" (which could be translated as "the land") necessarily refer to the entire planet.
With this in mind, how would you understand Revelation 9:4?
Here are my thoughts on it: The passage really has nothing to do with whether or not there is any "grass of the earth" that could be harmed. The point here is that these are not ordinary locusts that do the things ordinary locusts ordinarily do—eat up ("harm") vegetation. Rather, these are "locusts" from the "bottomless pit" (the habitation of the vilest of wicked spirits), and their mission is to torment the ungodly. This is the first of the three "woes" and is a part of the divine judgment that will be poured out on the ungodly just before the Second Coming. The object of this and the "woes" to follow is not merely to make the ungodly suffer but to (hopefully) bring them to repentance (cf. verse 20).
Now, what about Revelation 8:4. Does this verse tell us that all the green grass on our planet will be burned up?
Remember, John is describing what he is seeing (or has seen). When he says, "and all green grass was burned up" (Revelation 8:4), he is describing what he saw in the vision. He is not necessarily saying that all the green grass of planet earth was burned up, just that all the green grass he saw in the vision was burned up. This is not necessarily a global scene. The trumpet judgments lead up to the fall of the "great city" (11:7–8, 13), which may be understood as the worldly system's seat of power, so it is quite possible that the destruction described here has geographical limitations.
In any case, the answer to your question lies in understanding the literal meaning behind the highly figurative description of "locusts" instructed, "not to harm the grass of the earth or any green plant or any tree, but only those people who do not have the seal of God on their foreheads."