I'm a fine one to tell other people how to write - I'm still learning and will be until the day I cark it - which at my age mightn't be too far away :)
However, here are some tips for someone who might like to have a go and why not? As "they" say, you'll never know until you try!
Firstly, read read read!
Most authors write what they enjoy reading, so I would suggest that initially you focus on crime, romance, historical - whatever your "bag" is. After you have decided what you want to write, then you have to learn to write it!
While you're reading observe how the author phrases imagery, how dialogue is dealt with. Decide what you like about the book you are reading - does it feel good and would you write in that style? I don't mean copy or plagarise of course, just think about how you would write the same book.
You need to join a writer's workshop group, this is a fantastic way to try your writing out, perhaps with short stories first, and receive critique from your peers. You will also get the opportunity to give your own critique of their writing. This is a fabulous way to learn how to write and decide which genre you want to try.
A good way to learn is to start writing drabbles - 100 word complete stories - and then droubles - 200 word complete stories. These are invaluable for practice in tightening up manuscripts.
One of the common problems with which I wrestled and still do, is passive vs active writing.
Passive: E.g. The dog was chasing the rabbit as fast as he could.
Active: The dog chased the rabbit at full speed.
Watch your "that" and "which" - a common fault of mine is getting them mixed up - and for goodness sake do NOT use "You done good" and drop your "ly" at the end of the words when they're called for!
So - go to it and good luck :)