Please forgive the long reply in advance.
Your mind can be seen as split into the conscious and the subconscious, the conscious deals mainly with ideas, images, events, real tangible stuff, whilst the subconscious mainly in emotion and feeling. As far as I get it, whilst you are in REM sleep your subconscious mind is processing your recent thoughts, feelings and experiences, and your dreams are your conscious mind trying to interpret this process, so it is your conscious mind's interpretation of your subconscious mind's understanding of the experiences of your conscious mind, imagine using google translate on a page of text, from English to Chinese and back to English, that's kinda whats going on. The reason dreams are valuable is because it is the most direct look we get at our own subconscious, i.e. at our own thoughts and feelings, all we have to do is reverse the translation by 1 step and then put that into context.
So, say I dream about running from something, and the feeling that dream gives me is of fear, my conscious mind grabbed an image or scenario that it relates to the feelings and ideas my subconscious was processing at the time, so what is running away? It could be that im scared of or avoiding something, or that I feel pressured by something, backed into a corner and all I want to do is run away, so to figure out what specifically it is, I just need to look at my recent memory and find context, why would I feel like I'm avoiding something or being hounded by something? Oh yea, my last week at work has been so busy I feel like I cant turn around without someone wanting a piece of me, hence the feeling of being pursed and thus the dream.
The above was a simplistic example, but the same idea can decode most dreams and give you a very literal and obvious look into how things are making you feel. Interpreting your own dreams shouldn't be TOO difficult as each translation was made with your own interpretations and associations and your mind knows it all anyway, you just need to be open to figuring it out.
There are only 2 parts of my dream life that I don't fully understand (or cant decide upon):
1) I had a couple of lucid dreams, each time my best friend (dead) appeared in the dream and the whole dream stopped, I had no control over the dream (as many people say you do in lucid dreams) but I was awake and aware I was dreaming, and I chatted with my friend, no dream has ever felt that real, the dream itself felt fake as hell, but he and our conversation felt real. It was like someone else popped in and put the dream on pause to say hi. I was convinced before, but now I just kind of hope that it was really my friend saying hello from... well, you know.
2) I had a series of dreams at university which I can only describe as malicious, they didnt seem to relate to anything else in my life, and unlike most dreams which seem to start in the middle, these all started very mundanely at the beginning and grew naturally, they seemed to be tailor made to guidedly and naturally form a single negative emotion so powerful that it stuck with me for the rest of the day. Depression, Loss and pure murderous Hatred are the ones I remember. The Hatred one focused on a housemate, we got on quite well, but after that dream I struggled to look him in the eye for the rest of the day, I ended up just avoiding him, the first time I saw him that day I felt a powerful urge to attack him, each dream was so well orchestrated and well thought out, it was weird.
So, aside from those two examples, I think dreams are pretty straightforward and useful, something to be used as a diagnostic tool for your own problems, or a way of gauging your mental state.
Again, sorry for the long reply.