I consider the Synoptic gospels (Matthew, Mark and Luke) to be the heart of the Bible. I take this view because they give us the teachings of Jesus, our Examplar. I'd suggest it would follow that if we are serious about following Jesus, paying attention to his teachings in the books should be our first priority. You may notice that I've separated the Synoptics from the Gospel of John. This is not because John is in any work an inferior book or that it gives an inferior view of Jesus. I just tend to think that the Synoptics are "more earthy" and that because of this they are more accessible, not to mention more practical. I also believe that the Synoptics provide a much more literal account of Jesus ministry.
Conservative Christians (and others, for that matter) may be interested in knowing how I try to interpret the Synoptic gospels, so I'll try to provide a few principles I use off the top of my head. Unfortunately, I won't provide Scripture examples of these principles, but may try to do so later.
1. Jesus is not quoted verbatim when the authors record his teachings - I would have thought this would have been fairly obvious, but just in case this point is in question, you should try to read "parallel accounts" of the same event or teaching. If you do, you'll notice there will be slight variations in the text. Parts of a teaching that are in one gospel will be left out in another gospel. Sometimes two different teachings will be merged together.
2. Notwithstanding that Jesus is not being quoted verbatim, the authors of the Synoptics are faithfully quoting the substance of Jesus teachings - While the exact words may not perfectly represent what Jesus said, I would suggest that on the whole, the ideas and principles that Jesus wants to express are kept intact by the authors. Of course, there are many scholars who would disagree with this assessment, for instance those who suggest that Matthew 25 is merely Matthew's anti-Semitic rant projected onto Jesus. While this could possibly be true, I tend to err on the side of caution and assume that teachings attributed to Jesus are actually authentic unless there is compelling evidence to the contrary.
3. Because it is the substance of Jesus teachings that are recorded and not the exact words used, we should focus on the general substance of the teaching, rather than agonise over the semantic terms - I'd suggest that it is entirely counterproductive getting caught up on a particular word that may or may not have been uttered by Jesus. Besides, Jesus teachings were for his audience first and foremost, and I find it hard to believe that he would have expected the peasants who listened to him to deconstruct a word to find it's six possible meanings.]
4. The authors of the Synoptics each have an agenda of their own - While I believe that the authors of the Synoptics are faithful witnesses, there are writing because they want their audience to believe. They also want to stress different aspects of Jesus' person. Not that there is anything wrong with this, but it's something to which we should be mindful.
5. When a particular expression is only used in one gospel, it's more likely to be the author's own "spin". Conversely, when an expression is exactly the same in all three Synoptics, the more likely it is to be the actual words of Jesus - It should be pointed out, however, that when an expression is identical in both Matthew and Luke, but not Mark, Q is probably responsible and the authors have simply copied this source word for word.
6. Jesus needs to be understand within the context of his culture - Jesus was not a Christian, but was rather a Jew speaking to Jews. Thus, an understanding of first century Jewish culture and theology is necessary to understand Jesus, notwithstanding the fact that Jesus clearly transcended many of the paradigms of his day.
7. Jesus was not omniscient in any meaningful sense - I can see why people can get uptight about this claim, because they think it might impact upon Jesus' divinity. However, I'd suggest that few people would make claim that the earthly incarnation of Jesus is omnipotent. Scripture also makes reference to Jesus "growing in knowledge", which seems to infer that at least at one point in time, Jesus was not omniscient. For this reason, I have no problem with the idea that Jesus was wrong when he stated that the mustard seed is the smallest seed. However, I would suggest that Jesus moral teaching, properly understood, is infallible.
Anyway, here are a few thoughts of mine on the subject. I'd be interested in hearing your thoughts too.