Firstly, no need to worry about always coloring in the mouths. If you look over at CLAMP's artwork you can see that the characters' mouths are left white, along with Fruit's Basket and a few other manga. So it's all right if you forget every once in a while. ^^
Anyway critique time. Much better with the hands, and yes thumbs are tricky. The only reason it looks "wrong" for those who look closely is you made the thumb start a wee bit too high. But you're very close. ^^ I also really like the way you did her hair and shading, makes it more CLAMP-like. (Seeing that is Sakura my FAVE character of all time) Although there are a couple spots where you could've made the shades a little darker like you did at the one ruffle for the blue. The cherry blossoms also look lovely. However since it has a very similar shade to the skin....hmm....I think that's good. Since I recall something I read about colors from a link someone posted on this site. I'll go look for the link.
Here it is. I forgot which thread had it though. *sweatdrops* Thank goodness I remembered the title.
http://purplekecleon.deviantart.com/art ... -184642625There. You'll understand what I mean regarding the skin and cherry blossoms colors.
Anyway on with the critique. Hmm. Her chest looks a bit off. I'm not sure how though. Maybe it's because of the way she's standing or facing....or the clothes. I'm going to have to look at other pictures of girls just to make sure since my eyes fool me sometimes.....wait wait wait! I think I see it!
Where's her center? I understand her head is slightly turned. Then there's the center between the collar bone. Which doesn't match up to the center between her chest and the bow you have around her waist. (Again I say my eyes could be fooling me) That might be why it seems a little off to me. Still going to look at other girls though just to be extra sure.
PS. She looks more like she's cosplaying as Alice. XF (And might download if that's all right with you for background on laptop)