Here's my second story.  C+C is welcome, in fact, it's begged 
for!  Please let
me know HOW to make this story longer, or if it SHOULDN'T be longer.

Glad to oblige!

remembering the dream again.  Akane.  She was in her yellow 
nightgown and

Akane is almost always depicted wearing loose pajamas, not a
nightgown.

And why couldn't he get her image out of his mind.

You need a question mark on the end of this.

     Ranma walked quietly down the hall to Akane's room.  He 
was so lost in
his  thoughts that he didn't notice her until he bumped into her.

This doesn't seem likely.  Thinking about what?  I think it'd work
better if they notice each other and stop when they're two feet away
from each other.

     Their eyes met for a moment, just a moment.  Then Ranma 
looked away.
There was more in her eyes than words could ever say.
     "Good night, Akane," he said.
     "Good night, Ranma."
     And with one last look at each other, they went back to bed.

If the dreams were meant to predict this moment, Ranma should have
been wearing his muscle t-shirt and boxers in Akane's dream.  This
is what he usually sleeps in.

This seems about the right length, for the romantic, WAFFy story
you're trying for.  It might be improved if you work on the ending
just a bit, but you'll probably end up adding no more than two
additional sentences.  I think you want something like this:

    Their eyes met.  Neither looked away.  After a minute or two,
    Ranma made a tentative movement with one hand, towards Akane,
    but stopped.  Both blushed and looked away.
    "Good night, Akane," Ranma said.
    "Good night, Ranma."

(This is just a sample.)  Your story stands or falls in the reader's
estimation based on this moment.  You need to make the reader feel
something here.  You should rewrite and rework this scene over and over,
trying to get it exactly right.

If I remember right, one of Joseph Palmer's "Season"s stories (Winter?)
is something like this, but the ending effect is more profound than
yours:  the reader is aware that both characters have experienced a
significant moment in their relationship.  You might want to study
his story carefully, to see how Palmer achieved his effect.

Also, I think you need to decide if Ranma and Akane are dreaming of
this meeting precognitively, or just dreaming of each other.  The
clues you give, their clothes, imply that Ranma is dreaming of this
meeting, but Akane of Ranma generally.  The effect will be better
if they're both dreaming the same way.