Firstly I am a firm believer that everyone has a story in them – not everyone is a natural writer, granted, nor is everyone confident about spinning a yarn or recalling witty anecdotes in front of people. But everyone can tell a tale.
Some people have lived extraordinary lives, and are able to base their books on their own personal experiences. This of course helps with details and developing a rapport with the characters, making the plot seem real to the reader. Others have crossed paths with weird and wonderful people; those who you meet and can't help but wonder what happened in their lives to make them the people they are. One of the great wonders of the human race is it's ability to diversify. Others haven't lived a life that they could base the foundations of a book upon – but they will have come across other stories on a frequent basis. These stories may have sparked their creativity, or even allowed their mind to dissect the story and pull it apart. This is a great opportunity to rebuild in your mould, turning the basis of one story into something completely different, which you believe is better.
So when you have your idea for a story, where do you start? The logical approach to writing a novel is to start at the beginning. In my opinion, this is wrong! Why? Basically, because the chances are that the start of your story, if you are brutally honest, just isn't that interesting. The part people tend to start stories from in their minds is the end; how the hero overcomes the odds to defeat the villain; the plot twist which makes it unique; the person responsible for the 'whodunnit'. If in your mind the spark of a story is the end, then if you start writing from the beginning, chances are you won't make it to the end.
This is where so many 'budding' authors go wrong. Writing a story is hard work, and takes dedication. If you start writing the story at the start, this will probably be the boring part – character background, plot setting etc. Basically detail and setting. This is not fun to write, hence why so many give up!
Instead write the interesting parts first. Write the main battle scene; the death of a key character; the gory or funny aspects. These are parts which will get your creative juices flowing, and ultimately excite you, meaning you are more likely to dedicate time to doing it. Once these parts are done, then you will have already committed a significant amount of time to the novel – and the rest will be far more likely to fall into place.
Personally when writing Salvation, I had 4 chapters in my mind at the start. The book ended up as 36 in total. These 4 chapters weren't 1-4, nor 32-36; they were dotted around. I wrote each one as best I could, then started to link them up. As I went I would develop the story further, expanding the world I was creating. The other advantage to this is when you suffer from the dreaded 'writers block', you have your favourite chapters already written, which you can turn to for creativity, or give yourself a break from writing and put your 'editing' hat on instead.
Writing is hard work, and seeing a novel through to the end is very difficult. Give yourself the best chance you can and write what excites you first. Then you just have to stick with it – good luck!