Getting published is a magnificent feat!  However, it takes a lot of hard work to get your book out there.  One good tip I can give you if you want to get published is to first post your novel on a writing website.  It is preferable if you do this as you are still writing so that you can post a chapter a week and gain a larger audience over time.  However, you can also do this if you have finished your book by just posting a chapter a week.  One good writing site I can suggest is wattpad.com.  This site allows you to post your writing while also talking to other writers and advertising your story in the different clubs that are offered.  Many writers have gained a large fan base due to this site.  

This is probably one of the best tips that I have ever received.  So many novels out there are bland because they lack the pizzazz that is ever present in movies and on TV.  But some novels are wonderful because they are filled with details which makes them easy to picture and play out in your mind.  When you are writing you should always add a lot of details because this will help to hook in your readers better and leave them thirsting for more!  

Here is an example: 
First Version - Henry went to the market and someone hit his car.
Second Version - When Henry drove to the market on a cloudy morning, begrudgingly going to get his wife a quart of milk.  He made a point to park farther down the parking lot so that he wouldn't have any trouble pulling into a tight space.  Once he made it into the chilly market and fought through the crowds of busy shopping moms and eventually purchased his milk, he felt a sinking feeling in his stomach.  He had always been good with his intuition, but he waved it off as though it didn't matter.  However, as he marched across the crowded parking lot, a rock somehow managing to get in his shoe and worsening his mood, he saw from a distance a clumsy teenager trying to pull into the parking spot next to his car...but they didn't make it.  Instead they rammed their souped up corvette into his station wagon, causing their airbag to erupt.  Henry stopped in his tracks and dropped the milk to the cement with a thud, the carton opening and spilling all over his shoes.  He knew that his day could now not get any worse.

Doesn't the second version sound much better?  You can completely picture the scene and it doesn't leave the reader responsible for imagining up the scene themselves.  Remember this tip in every writing piece that you pursue and you are sure to have a winner every time!  

When I was in school an author came to talk to my class and she gave me one of the most important tips that I still continue to use today.  

Keep a journal with you always and write down observations that you have and can use in writing later. 

If anyone asked me the most important thing to writing my answer would be "always rewrite".  Writing is a process and rarely what you write is perfect the first time around.  I have found that when I rewrite something that I have written over and over again I tend to like my writing and characters more because I am better able to describe the situations clearly and with more description than what I started with.  I also find that when I rewrite I can take out unneeded information that would only burden the reader.
When I first started rewriting I found it to be a very terrible task and I honestly hated it!  But over time I have found that it is the most enjoyable part of writing because you are able to not only rewrite a better piece of writing, but you are able to read your own writing over and over again and in turn become accustomed to yourself as a writer.  Reading and writing go hand in hand and if you take time to reread your writing over and over and rewrite it you will find that you have taught yourself to become a better writer all on your own just by becoming more acquainted with your own work.