When critiquing a song, I try to:

1.  State whether or not the song is in my preferred genre, hence letting the artist know how big of a "grain of salt" to take the comments with.

2.  State, as a whole, how much I liked the song, hence letting the artist know how relatively severe my subsequent comments will be.
     For instance, if a think a song is near flawless, I may still make a minor suggestion like "the guitar tone didn't fit..." But it's really just nit-picking for the sake of improvement, no matter how small of a detail it is.  This is just for the sake of the perfectionist who still seeks improvement. 
     On the other hand, if I didn't like a song much (and say so), then the "guitar tone" comment could likely be the reason for my disdain.  Therefore, I might recommend that the song be re-done with a different tone.

3.  State at least one specific thing you liked about the song.  (See #2)

4.  State at least one specific thing you thought should be impoved.  (See #2)

5.  Sometimes I just plain out forget to vote.  I am going to include that in step 5. 

Just my USD 1/50

Anyone got any more to add to what's been said?

Try to remember when voting, and critiquing, that this site isn't all about great production, and true studio quality... It isn't a showcase site for the best of the best, It isn't going to get you a record deal..  This is a site for Musicians to help one another, talk with one another, feed from one another.... and It is for Beginning Musicians to get their feet wet, and learn from the old dogs....  I think many lose site of that....  So when giving critiques, take into account the comments made by the artist, perhaps they are a begginner, perhaps they have made comments that will let you know why certain parts sound different, or off time, or dissonant..  Don't ruch a critique because "You know what's best" or because "It's crap" listen completely, read, and most of all, feel..

 When I critique a song, I literally close my eyes, tune out the world, and LISTEN.. Then I read the comments left by the artist and others... Then I listen AGAIN... THis gives me two advantages, one I had a totally unbiased listen, no insight, no comments about anything.... second, I now know what they want me to know, and listening a second time, I also hear things Imissed, and understand parts I was unsure about... NOW I am ready to critique...  Voting goes without saying, it is part of what we do...  I vote, especially if in a battle...  It is my duty as a member of the site to participate... In order to participate, I must participate in ALL aspects, not just the ones that benefit me...  Besides, Voting actually does benefit me.. because when someone wins the battle, I helped make that possible, and who knows, one day maybe I will win... would be nice... Jut for fun mind ya.... 
                  JimK