Greetings,
  Well I have been lurking on the FFML for over two years, and have
collected quit a library of fanfics
from all kinds of places. Recently I started acting as a proof reader for a
group of writers here in 
Japan, after which I started making comments to some other writers on the
FFML. Well after much consideration
I decided I could probable share this with everybody.
  There are many great fanfics out there, but there could be more. One of
the big things that detracts from a
good story is a lack of believability, or plausibility. Even in the Ranma
universe People will act in certain ways
when provided certain situations. I have seen many fics especially
resolution fics, Where the do not show realistic
results. An example is if Ranma married Uykou instead of Akane how the
Tendous would react. The would still not be
friends with Ranma unless you can come up with a good reason for it. Most
people have characters care on as friends
after situations where in real life people would be out to kill people. And
writers can't use this is the Ranma, 
universe or something like that because an prime example is Uykou spending
10 years trying to hunt down Ranma to 
kill him. Other caracters would have even more extreme reactions then Uykou
did for some of the actions I have
seen in some fanfics and the carry on as nothing had happened.
 Another big problem is that people change peoples opinions and attitude
with out giving a reason or a good reason.
People for the most part do not change for no reason or another. This
mainly affects Resolution fics, as a lot of writers
will have say Ranma marry some one other then Akane with out giving a good
reason for his his change of heart. A 
prime example of this is "College years", a post manga story where Ranma
marries Uykou with no reason why he dropped 
Akane after what the had been trough. At the end of the manga it is quit
clear Ranma and Akane are in love. This fic also
fails because it also does not have plausible character reactions. After
being dumped everyone is still friends and Uykou
and Akane are Roommante in college, not very believable. A good resolution
fic that gives Ranma to someone else is Lawsons
"Roses in the Shadow" where the reasons for Ranmas change of heart is
explained, and the other characters have plausible
reactions to them. Even in Comedies such as Ranma 1/2 there are causes for
events and peoples reactions may be way out of
proportion to events the are plausible. 
 Well that is all for now, maybe more forthcoming
-Peace