To the people who gave all the good tips:
First of all thank you for your cooperation.
Second, I have seen all your comments and decided to put only a few here, because you basically all think the same about how a reader should comment. 
The comments that are posted in here are pretty much a summary of what you all would like from a reader. (:

 

To the readers:

dream_keeper88  on May 27, 2013 01:34:32 says: 
giraffe-hugger unnie uses the sandwich principle: say something nice first, what you like about the story, then dive into the areas which the author might need improvement or a part in the story which confused you and then end it with an encouragement.

Ex. "Yay! Thanks for the update. I really cracked up at that scene when ____. Definitely love how you wrote that. But, why is ____? I thought in the previous chappy he ___. Anyway, just keep writing coz I like it so far."

Or if you really like the author's style: "Thanks for the update. I really like your writing style. The words just flow right into each other and the scenes you described were so real to me. Your characters are so realistically depicted, that I could totally see this in a movie inside my head. Continue writing and I will continue reading."

If the author didn't edit the chapter: "Hey, thanks for this. No need to rush though. I spotted a couple of typos here and there, a bit distracting at some point. Your story is good and is definitely worth the wait so just write at your pace. Oh, loved how he apologized to her."

If it's a story a newbie wrote: "Welcome to AFF! I hope you enjoyed it here so far. The plot might be a bit cliche but I am certain you have twists in store for your readers. And before posting, edit it first by running a spellcheck and grammar check. Doesn't have to be perfect, just reader-friendly. Wouldn't want readers to be reading a completely different story from what we are writing. Nice start. Keep writing and learning :)"

An author gives at least a thousand words per update. We could at least come up with a sentence to just show our gratitude and give them motivation. A writer often starts writing from himself/herself. You would notice it in the frequency of his/her updates in the first few chappies. But it kinda dwindles towards the middle. It takes both motivation and discipline. And it is the readers that could provide part of that motivation.

 

Love4Minute2NE1  on May 27, 2013 00:18:17 says: 
Authors like feedback as it encourages them to continue writing because they know that a reader likes what they've written. Simple things such as "I really liked how ____'s character is portrayed" or "The way you describe things" is nice. That is positive feedback but you can also include constructive feedback such as "I think you should fix your awkward formatting to make it smoother" or "You used that puctuation mark wrong" are good too and always make sure to point out the mistake to help the author. 

Acknoledging what is written in the chapter update is nice as well such as "Oh gosh, now they're on their first date together!" or "I wonder what happens next now that ____ disappeared". Some authors keep certain things hidden in their writing for a reader to investigate and try to crack down what's inside so analyzing makes the author feel like the reader is actually absorbed in their writing. An example would be "____'s character was in the house right before the window glass shattered. I think ____ is responsible for the robbery." or "____ is obviously in love with ____, just look at the way he looks at her!". Those, I believe are good ways of posting a comment instead of the plain "update soon". 

Btw, the blanks in my comment below aren't curse words but are just there for you to replace it with a character's name. ^^

-Ritsu  on May 26, 2013 21:21:31 says: 
Something I love is constructive criticism. When they tell you what they thought on the chapter, how it made them feel, something on the characters/plot. Something that SHOWS they actually read it. Not a one liner like, 'love it, update soon author-nim!'

So whenever i get a longer cc comment, i feel no need to get any others. A comment like that makes an author satisfied and better understand something from a reader's point of view.