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First thing that comes to mind is the guys arems aren't long enough - the rule is elbows just above hips and fingers reach halfway along thighs. Somehow it dosen't jump out as much for the girl, but hers are a little short too.
The spikey bunches look good at this stage, as does the guys hair, but then it's a very loose layout sketch so there's little I can say on that for now. There are many approaches to drawing hair, I think these styles would look good in the feathery many strands drawn style, rather than a fairly solid style - what's your plan?
Ah, maybe her hair is a little small for her head. At least in comparison to the guy's hair:head proportions. She'll have a large forehead.
Oh, and the girl is a little taller than the guy. Maybe that's the plan, just thought I'd mention it.
The guys legs look the correct width and are attached suitably to his body, nothing I've got to say in that sense. Both anatomies look pretty awesome, I for one have massive panick attacks with attaching arms to shoulders without making someone look like a box. Yours look great, perhaps the girls are a little too folded back, even though she's got her arms behind her back.
There is something a little odd about the girl's body, I can't quite put my finger on it. Maybe her lower arm is just a little lumpy and is confusing me.
I might have a go at some redlining on stuff I've said, but clearly not in red... but I've never convinced my mouse to cooperate on this sort of thing, so you might have to do with the essay I've just written.