? 
The question you are asking is not new. I have asked it. Perhaps anyone who has written has asked the same questions you are asking. And there are tons of people who have written about the questions you are asking:
Start from this link:
http://www.scifidimensions.com/Mar02/howtowrite.htm
Truthfully, nobody can really teach you how to write. These are only guidelines, suggestions and
tricks of the trade to help a fledgling author over a few of the humps we have
all battled. Godspeed, and good luck.
RULE #1 - WRITE!
All the time, everywhere.
Make the time. Cancel dates,
forget TV, pass-by books and hot sex with the twins down the hallway. A writer writes. If you're not totally committed to Rule #1,
then don't bother reading any further and please pass this on to a friend who
really wants to become an author.
RULE #2 - WRITE IN YOUR OWN VOICE
Sounds silly, I know, but writing is one art form where it is generally
best to shoot from the heart. Nothing
fancy. Don't wax didactic with
palliardic xenophobes, if this is not how you normally talk (or even if you do). And don't try to write up to the reader, or
down to him either. One will only make
you a fool, the other - pompous. Neither
will get you sold. It also wastes a lot
of energy you'll need for other things.
The idea is really very simple.
If you can tell an interesting story, then you can write an interesting
story. However, if your friends hate the
way you meander through a joke, or the plethora of unnecessary details you added
to that fishing trip tale, then these are major danger points to watch out
for.
Just be yourself. If you have something to say, eventually it will come
out.