Here is the constructive critique you wanted:

Well it seems that the facial proportions are not to bad except the mouth looks a little off centered. The biggest problem I am seeing is that the picture is coming off to flat. This is due that you are trying to make your shading all smooth and is just graying out the image, don't be afraid of letting some of that paper show through for the highlights.

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ah. i see. thank you very much~~ ^^

Nice job! and for your first portrait, it is very well done. A few suggestions I might give include the overall use of value, sharpness and contrast. All the grays really seem like the same value, and it would make the figure pop even more to vary your grays, along with using dark darks and light lights. That is where the contrast comes in. It can help to distinguish your figure from the ground. Also, it is a fairly blurry image, and so sharpening up just a few things around the face and a few edges can really add a nice play of blurred versus defined edges Keep up the good work

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^^ thank you! i'll keep that in mind! contrast, sharper lines, more variety. got it. thanks~~