In the first place, much of the Bible can only be taken literally, even if the reader doesn't believe what he's reading. The Bible is a historical account (past, present, and future) of God's dealings with man. From a historical perspective, the Bible can be very detailed: for example, in Luke's account of the Nativity, we're told that it happened when Augustus was Caesar; and, to be more specific, when Cyrenius was Governor of Syria (Luke 2:1, 2). That is an obvious reference to a very specific period of time, and it would be illogical to take it as a "figurative" or "symbolic" statement. Similarly, the records of the kings, or the military statistics, found in the Old Testament are meant to be taken literally. One can argue that they're not accurate history, if one is so inclined; but history is what they are.
On the other hand, it would be foolish to adhere to an absolutely literal interpretation of every word in the Bible. Jesus says, Verily, verily, I say unto you, I am the door of the sheep (John 10:7). As someone has pointed out, this doesn't mean that Jesus had hinges and a doorknob! He was obviously speaking figuratively; but the meaning of what He said (that He is the only entrance to Heaven) should be taken as literal truth: Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me (John 14:6).
Everyone who doubts the Bible has their own favorite objections. Are we to believe that Jonah literally survived three days in the belly of the whale? Well, why not? There have been other historical accounts of such things happening, and, although being swallowed by a whale would undoubtedly be fatal in most cases, we have no empirical evidence that death would be inevitable in three days. In this particular case, it's worth noting that Jesus Christ Himself took the passage literally: He said, For as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth (Matthew 12:40).
But what about all the weird things that the prophets saw? Are we to take them literally? When Ezekiel saw the strange creatures, or the "wheel in the middle of a wheel" (Ezekiel chapter 1), were those real, literal objects floating in the sky? As a Bible believer, I think they could have been, but I don't think it's necessary to believe that they were. The chapter begins, ...the heavens were opened, and I saw visions of God (Ezekiel 1:1). Likewise, John had visions of many things when he was on the isle of Patmos, writing Revelation: but in both cases, the Bible clearly indicates that these were visions, given by God. Do I believe that there were mysterious physical wheels hovering in the air over Ezekiel's head? Maybe, maybe not. But I literally believe that those were some of the things that Ezekiel saw.
This brings us to a crucial point, which was pointed out to me many years ago by a wise teacher: the words "literal" and "physical" are not synonymous. Something can be literally true, without being physically true in the space-time continuum where we live. A good example might be Moses' burning bush. And the angel of the LORD appeared unto him in a flame of fire out of the midst of a bush: and he looked, and, behold, the bush burned with fire, and the bush was not consumed (Exodus 3:2). Was the fire literal? Yes, it was certainly literal enough for Moses to see. Was it physical? I think not, because if it had been, the bush would have been consumed.
The notion of something being literal, but not physical, is hard for the Gentile mind to grasp, although I'm told that Jews have an easier time of it. But it shouldn't come as any surprise to a man or woman who has received Jesus Christ according to John 1:12 and John 3:3-7. We believe that the Holy Spirit of God lives within our bodies. He is literally inside the body of every Christian. But is His Presence a physical thing, that can be seen on an X-ray or in a blood sample? Of course not. In a similar, although horrible, manner, a man or woman can have unclean spirits, also known as demons, inside their bodies: but their literal presence isn't physical - - - it's spiritual. And spiritual realities supercede even physical realities. I don't often quote rock & roll songs, but years ago, a band called The Police sang "We Are Spirits in the Material World." Every human being has an inherent knowledge of this truth, even if they fight against it, and declare themselves "materialists." And it doesn't just apply to "religious" matters. A young man thinks of a certain young woman, and suddenly realizes, "I don't just 'like' her; I'm literally in love with her!" Well, of course his love is literal: it's just not physical, although it may be expressed physically.
When one approaches the Bible, and seeks with a sincere and humble heart to understand it, the best rule of thumb is this: Interpret any word or verse or passage literally, unless it is completely impossible to do so: for example, in the above illustration of Jesus having hinges and a doorknob. If it says that, in Noah's time, the whole earth was flooded, accept that as a literal truth, and don't believe the intellectual pygmies, proclaiming themselves to be "scholars," who say it was merely a "local" flood. When God says that Moses crossed the Red Sea, He doesn't mean "the sea of reeds," as the intellectual pygmies claim; if that's what He had wanted to say, that's what He would have said.
And if someone asks if you believe the Bible is literally true, simply smile, and ask courteously, "Of course! Don't you?"