Having been through the experience of writing a novel I can look back and share my experiences and have two pieces of advice.  First of all write it.  Two pages a day, every day until it's done.  Then after you've seen the mirage hinting at a drink of water after your trek through the desert which are the words The End, the real work begins.  

It's a bummer that those of us who are most creative are the least business minded, and generally the opposite is true as well.  Presenting our work in a methodical manner, keeping track of what query's work well and which don't, which agents we've queried already and which are still on our list is mind-numbing compared to actually writing our characters lives.  Receiving what can seem like an endless supply of 'No thank you's' can chaff the skin a bit.  None of it is easy but there are tools and people to help.

The tool that I have used the most and has been the most effective for me is QueryTracker.com.  Huge list of resources there for writers.  Everything from help pages on writing querys, forums for testing them out and getting feedback, and the most important part which is the lists of agents and their contact info.  If you haven't been there definitely go.  

Scratch  

How do I get ideas on what to write about?  I like to drop two characters into a living room and get them talking and then learn a bit about them as they talk.  Each asks questions like you or I would and the other is forced to answer the same way.  "So, what do you do for a living?" or "Did you hear that explosion last night?" each forces an answer and any answer will work.  Just play it out.  It's a bit like Mad Libs. I usually know what kind of 'world' I'm in at least whether it's fantasy, real or time-shifted at least but after that I like to let them get me started.  

Adding a third or fourth person to the conversation helps hone your dialogue skills and creates more complex situations which can help you find something interesting to talk about.  My Characters often describe themselves.  
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