I usually go with the teaser. This is a good example of my covers.14
There are lots of hints about the events of the chapter hidden in this cover 
I tend to go for teasers all the way, sometimes even taking exact scenes fron a future part of the chapter and just expanding it to a full sized page. I'd like to do some more abstract stuff with them, but at least when it comes to stuff like this, I'm far too literally minded to make it too out there. : P
My technique to making cover pages is lying down on the floor and crying (while maybe eating something).
Not really, I usually try to make cover pages hint at whats to come / what characters are going to be the main focus of said chapter. In general though I usually just wing it entirely and whatever image I like that fits the chapter the best I keep to use! There is no rhyme or reason here its just whatever I think looks pretty.
@UzukiCheverie I always enjoy your cover pages! They're always so interesting and different each chapter. It's cool that you do guest covers too!
@TrustyShamrock that's a cool idea! it's always nice to see how characters are when they're just hanging out ^.^
@igneriss it's good to draw what you feel like. I agree, all the techniques are fun to try~
@getsuart yay for teasers! I feel like this can be the hardest to pull off, depending on the story. How much hinting is too much? O.o that's the question I always ask myself, and then I end up doing something less teaser-y instead haha.
@Savannah oh man I envy you! I wish I could just draw what comes to mind. I tend to overthink things haha.
@joannekwan Oo I like that idea for Heavy Horns! That's a cool way in incorporate the story into the structure of the comic. Very cool!
@ashriott I think consistency can be a good thing when it comes to looking at a comic as a cohesive piece. Your technique sounds like a winner to me ^.^
@Longman I think the coolest thing about the teaser technique as a reader is when you go back and look at the cover at the end of the chapter and think "ooohhh that's what that is on the cover! Neato~"
@epiale yeah the abstract can be challenging. I haven't attempted it myself, but I'd like to! I think some stories lend themselves to the abstract covers more than others (e.g. Pandora Hearts).
@heterodont lol it's okay I lie down in my bed and cry while making cover pages. But yeah, making pretty covers is a good way to go. Pretty art is always a win ^.^
For Grassblades1, I tend to go with something that is representative of what happens in the chapter/is the theme of the chapter, without being too obvious or spoiler-y - which is a difficult balance to strike!
... And as it is a difficult balance, I thumbnail the heck out of everything before I settle on a final design. My first chapter cover went through seven versions before I landed on the one I went with.
Examples:
This is my main character (though we can't see his face), with his right hand on the sword that is very, very important to him. There's a significance to it being his right hand, and the scrap of cloth tied to the sword is the same colour as a piece of clothing the second main character wears, and there's a significance to the beads as well, but that hasn't come up yet. I like working non-obvious symbols into the covers, because it gives people things to wonder about, AND it gives readers the chance to go "Oh, so THAT'S what that means!" once the thing is revealed.
Part two - it's the sword again, because that's important, but there's also a lot of blood (because there is more blood in the chapter), and the rest of the items scattered around are references to things that appear in the chapter, AND new characters.
At some point, I probably will draw a cover on which my main characters can actually be seen, but my cover-designs are usually more inspired by book-covers than my comics-covers, and book-covers tend to be less focused on featuring their main characters.
For Shadosassins1 I usually try to show my main characters posed in an environment that you'll see during the chapter. It's almost like a small teaser into the chapter. However for my chapter 3 cover, being the fighting game fanboy that I am, I created a cover that resembled a poster or game cover. Luckily, it fit my story like a glove. I don't know, I'll probably still do later chapters with the same environmental style that I done before, but I liked the idea of experimenting with something off the wall.
My cover I went with something bright and colorful, while having the main character have a more unhappy expression on his face to create a humorous contrast. The pose that the main character is in is also a homage to lard lad.
It does not give away much of what the story is about but that was intentional. I don't want to give away the whole story with the cover, instead I want to give readers an idea of what the tone and atmosphere of the book.
Also there is a cat on the cover because people love cats.
@AnnaLandin wow! seven versions? dang! But the results speak for themselves; it's an awesome cover! I appreciate how much thought you put into the details. Small things like that have a huge impact for me as a reader (and as a fellow artist ^.^). I'm already subscribed to Grassblades, but if I weren't these covers would definitely entice me to check it out (and subsequently subscribe because it's an awesome comic).
@allenthomas I can definitely see the game cover influence! It reminds me of an epic Kung Fu movie cover.
@Neil_Harrington you can't go wrong with cats lol. And cats PLUS donuts? #winning. Speaking of cats and donuts, have you heard of donyatsu? It's an anime/manga about cats that get fused with donuts in a post-apocalyptic world. 
I generally do more abstract/aesthetic pieces with underlying themes that are relevant to the plot, or will be... and I like dynamic compositions with implied depth or motion. Stuff people might buy as a print or poster, or look good on the cover of a booklet. And definitely with a character or characters as the central focus. The colors in my cover artworks are usually pretty muted because I think it suits the theme of the comic better, but I like to have a concentration of color and detail in the middle/foreground of the piece and a more plain background to draw the eye to the character.
As a fan and a reader, I like pretty official artwork of my favorite characters more than anything, so I guess that's what's on my mind when I draw prints and covers hehe.
To be honest, I just draw pictures of various demons from the Ars Goetia. I guess it's kind of thematic...?
@Cielle Indeed, teasers are quite hard. As long as it isn't big shocking spoilers, I don't think it's a problem. Usually, I put characters that are coming up in the first half of the chapter, so you will still have a lot of big things to discover.
And when i don't have characters, I just sketch the main scenery. Or there will be simply items. 
13 days later
For "Summerdays"1 they are more conceptual. They don't have much to do with the story itself, but more with some concepts. Sometimes they feature small details that are important for the story or just fun and cute, sometimes they set the mood of the chapter or relationships. Also I try to choose different characters, I like asking my readers who they want to see on a cover of the next chapter, or ask my friends.
That's the newest
We haven't done a full 'episode' cover yet, but we do covers for our act breaks. It's been really interesting to read through people's opinions on the main covers though. Main covers always baffle me. I never know what to put on them. x.X
We're in the middle of trying to figure that out for both episode 1 and 2 on Kamikaze.
On our act breaks though, we do the teaser method. Objects of importance are featured with background images of import. It's simple, but a lot of our readers like to guess what the objects mean, or how it'll effect the story.
For example the pages for our first episode acts look like this:
Act 0
Act 1
Act 2
Act 3
Act 4
They're simple, but they work for us. 
This is the most recent cover I've done for Burning Bright; trying to keep things a little more simple, but still throwing a little teaser in their - trying to catch readers' interest.
mmm i try not to go too crazy in detail, i mean i would love to but i just know ill have a lot of covers to make so i try to make them look organized and simplistic. im going with that (one character a chapter) look right now, all traditional, copic marker.
@AngieVX those heart sunglasses are cute!
@Kamikaze I like your act-cover style! like you said, it's simple but effective! It makes you think and theorize~
@ErithEl I think it's a nice balance for a cover. From what I've read so far of Burning Bright (which is one of my favorite comics, BTW, just saying ;D) I think this cover hints at what's to come without giving anything away.
@zwebb90 I think going for a simple look is a-ok ^.^ sometimes less is more. Sometimes less is less. Each comic has it's own style, which is part of what makes it so fun! What works well for one comic/artist might not be what another comic/artist needs/wants.