A novelist gives himself or herself considerable room to manoeuver, in building up a plot and in fleshing out the characters. A short story writer does not have that luxury.  He or she has to say whatever a novelist would, but tersely, and in condensed form.  Non - fiction writers deal with history, current events and the increasingly popular genure of futurology, Autobiographies and biographies would also be covered by non - fiction, though a number of them are actually fictional.  In poetry the choice is basically between vers libre (free verse) and rhyme.  Playwriting would be almost  invariably in the fiction category, but could also be closely based on fact.  Overall, however, it must be remembered that the distinction between fact and fiction could be very narrow.

Writing, like everything else requires a certain amount of discipline.  According to what you are comfortable with, set yourself a daily minimum number of words.
Most writers these days write with their audience in mind.  Appealing to the lowest common denominator has its commercial rewards, but is intellectually dishonest and unsatisfying.

Your style of writing should be what suits you – short sentences, complex sentences, lyrical, compressed or expansive prose, level of experimentation with language, imagery, use of metaphors etc.  Anything goes, as long as you are good at it. Remember, it is impossible to write deathless prose all the time.

Finally, a word about publishing.  This could be the toughest part.  You would in all eventuality go through a series of rejections.  But don’t get disheartened, have faith in your ability and in your manuscript. While waiting for the right break with the publishers, start working on your next  manuscript.  This is the legacy you will be leaving your friends, family, the next generation and hopefully, the larger public as well. Your written words shall speak for you, when you are no longer there to articulate them. This is the closest one can get to immortality.