Good to see you trying out other methods; an aspiring artist should have some guts to give a shot at everything.
However, there are few things I would like to suggest:
1. Get proportions right
I know it is a total pain in the ass to get it right, but you should always practice the proportion of figures. So, please do not restrict yourself to a face; draw at least a half of a body.
2. About shading
You said shading with 0.5mm lead is fun. Congratulation, you just confessed you are a glutton for punishment. Especially when you are aiming for smooth texture, a mechanical pencil is NOT your friend.
In addition, the smoothing generally decrease the contrast of each shade and consequently, can ruin a good piece. So, I would hold myself back a bit with smoothing.

This was done fully with 0.5mm lead pencils - one with HB and other with 2B. For each part, I gave coat shading of 2B and smoothed the area with Q-Tips. Then I started to give contrasts and then smoothed
the area again with Q-Tips again. Rinse and repeat for about 3 times and you should have somewhat dark tone. This is where a HB comes in; this sucker requires a lot of pressure to get smudged. So restore
the desired contrast with a HB lead. Then grab an eraser to give highlights to finish it off. As you can see this is freaking painful and you should think about getting 4B or 6B pencil for shading. If you
don't lose your appetite for drawing after drawing a full figure along with background, damn it sir, you have great perseverance.
Hope this ranting helped and keep those hands busy.