I really like your style, guy! Nice choice of colors.
I wanted to say a couple of things about your large characters there.
I'll start from left to right, alright? First off, your self-insert.
-I don't really get this hairdo, but in any case, it kind of looks kind of uneven, like there's more on the right than on the left. That bottom corner towards the sideburn is kind of messy, too, and it has this circular-looking strand that looks a tad out of place.
-I don't use glasses or anything, but I think the bridge is supposed to be closer to the upper area.
-I think you could go a little easy with the sel-out, it can make your outlines jittery if you overdo it.
-I'm detecting a little unease with folds here. For the first guy, all those folds across his torso are a little excessive, and they might even be going on the wrong direction. For t-shirts, I'd say the hinge point is the chest since it has the highest elevation (generally), though it could be less slanted if it's a tighter shirt.
some examples:
1 2
I suggest you at least skim
this, it could be helpful.
-All that shading on the sleeve makes little sense to me, since the light should be hitting there. Also, the sleeve should be overlapping the torso, but it doesn't give that impression here (that black cluster there is clearly the culprit)
About the red/pink-headed guy(?)...
-I think you should move the mouth up by one pixel, since his face looks way too elongated that way.
-I think you should add more hair on the back, right now the shape makes it looks a tad uneven, like he's missing a part of his head.
And with regards to the other guy-- You used this sort of shading with the previous guy, but it's more evident here. It kind of seems as if that part is at a different elevation than the right half, not very natural, really.
I hope that wasn't too much at once. Welcome aboard!