This is kind of fun.
Is the character closest to the front of the picture the one holding the camera for a selfie? If so his arm is in a very awkward position and should be facing more towards the front instead of to the side. The line art is some of your best compared to more recent submissions that seem a bit blurry and sloppy. There's a few spots that could use slight touch ups such as the one finger on the closest characters hand has a line that's way too thick compared to the rest and the lines from what I can assume is some sort of hoody string goes into the finger line a little bit.
Is he thinking about watermelon? That's a weird food thought. I'm thinking it's actually pizza, but with how small the dots are it doesn't look like it's representing pepperoni so I'm going with watermelon here.
I don't like the term selfie in this picture since well... a selfie suggests that you are by yourself, hence the name... selfie. This is more of a togetherie. I imagine this is what a group of friends this age would do in a picture in real life so I think you've captured the feeling of friendship pretty good here.
It's like, alright everyone do something cool for the picture. Guy up front hasn't slept in a few days and gets the full wrath of the camera, two out of the remaining three do something cool, but the one guy has no clue what to do in the amount of time given so he gives the generic thumbs up.
So just some random stuff. The guy giving the thumbs up has an awkward stance. It seems like we should see more of his legs than what we see here. The guy doing the yoga type pose should probably have a part of his foot pop out somewhere, but it just kind of disappears. His toes should be popping out between the front arm and body of the guy up front.
I also think that there's too much empty space on top. If your picture was cut more like it's icon I think it would look a lot better. My eyes get drawn to this empty spot and am left with a feeling that there should be something there.
Overall, a fun picture. I like your style. It would be fun to see this one colored in and where you used dark thick lines for shadows like on the dabbers neck you could use some shading to represent the shadow instead.