 Critiques on large details on older stories can be useful; use your best judgment and remember that the author may have forgotten this story entirely or may already look back on the story with embarrassment.

Checking the publication date is key in all cases of leaving reviews, but especially in those leaving constructive critiques.  For example, if the dialogue and interests of a particular character seem strange, a quick check of the publication date may show that the story was written before the character even appeared in canon and was speculation based on a casting spoiler.  The feedback you leave can then alter from: "This character is completely OOC," to "I see that canon didn't end up supporting your speculation," with or without a discussion on whether or not the story still stands on its own merits after having been jossed.  (v. 1. Fanfiction term coined in Buffy: The Vampire Slayer fandom regarding fanfics whose plots were rendered AU by later canon developments, usually those written by showrunner Joss Whedon.)

Brief negative reviews can be helpful, if only for the information that a story didn't work.  Some helpful phrases:


The in-depth review list presented earlier is just as useful for a negative review as a positive one, although if you find multiple problems with a story, you may wish to focus on one or two particular aspects at a time, and give the author a chance to work piecemeal on improving her or his work.  If you have the time, offering to beta read future stories may help this process, although that may be more effort than you wish to expend.

Do not be afraid to leave negative reviews.  Do understand that authors will not always respond graciously to them.  If an author does respond in anger to you, ensure you haven't committed a faux pas in your review such as getting the details wrong yourself or submitting a not-review (see below), then decide if you wish to continue correspondence with the author.  Unless you are good friends with the author, you probably should not advise the adjustment of medication, but rest assured it will probably happen in good time.

While all feedback is in and of itself a good thing, there are certain things you should try to avoid in a review.  These are not comments on the story itself but bring in outside factors that are not necessarily related to the story's quality and could be perceived as needlessly inflammatory or even downright rude.  The following is a handy if incomplete list:

A review that consists entirely of relating how much you hate the primary pairing in the story unless it is followed by the words "but I really liked how you handled them here."  Taking a review space to tell the author how much you hate their favorite 'ship is not constructive, and it is poor manners. 