HELP, critique for (fast) improvement

As far as improving fast for coloring and rendering it comes down to mileage and doing lots of studies of the things you want to understand better.

As far as this piece is concerned, The anatomy and the perspective of the face are things I would look at. I did a quick PO

Try to make sure everything is following the same line of perspective on the face. I recommend drawing a box over your face and testing that things line up. This is a challenging angle so using reference can help a ton as well.

After you make sure you anatomy is correct, then you should add clothing over top. It'll help with understanding how folds work over top of the bodies form.

Other than those things, I like the colors here.

For the background you can just take a photo from google and blur it a lot. After the blur, you can take a soft brush and paint in some extra shapes if you choose. As far as rendering this piece. You should set up a 3 point light set up to start with.

The moon light coming from the top right is kinda like your sun light in another scene or even an directional light. Then we have the skylight which affects the top planes of the anatomy of your character. Last is the bounce light from the ground which is light opposite of the light rays coming from the Directional light(moon light in this case). The bounce light lights the bottom planes slightly. You can then add more lights like the rim light in this case. The rims can come from street lights that are just off canvas/camera of the scene light you have here.

By the way I just blurred a NYC picture for the background and did a slight paint over. This is just a way to get started. You can define things further if you want.

Hopefully that helps.

Sorry I don't have the time to do a paint over, so I;ll mainly write out what I see. You should get reference for the hands. Another thing you can do is have the feet point more downwards because it doesn't quiet feel that the feet are on the ground. This is a problem I have as well. I recommend changing the red on the cloth . It's really power in the scene. Its the first thing I see. Red is a really bold color so you gotta use it wisely. I think you can either make the red on the cloth the same off white color but with a red pattern or red logo or change the color to the green of the shirt. Unless your going to add more gold in other areas, the shoulder piece feels out of place.
Because you have this misty background, you probably won't get the strong blue light from the sky like you have here. In this setting it is probably very cloudy and you'll get a less saturated blue here kinda similar to your background. I highly recommend looking at reference for this one and defining your background a little better.
Besides all on this, I think you have a cool scene with interesting challenges. Just use more reference for each step. Your getting better. Keep it up.