Dafuk, its a troll smile

What is the reference picture? Can you post it here?

I think it's pretty good. My only comment is the hair could be more realistic as it now looks kinda one layered.

other medium maybe? try charcoal stick. the thick one for the hair. then rub off certain part to make the shining hair effect. Thats if you wanted the sketch to be more faster and less tiring

Get a sketchbook & just draw wherever you go; from reference in real world or photos if indoor.  Your skills will naturally gets better with more practice.  Visit gallery, art forums to see how other masters do it & learn from the best. Cheers!

I advise you to post your sketch here: https://www.deviantart.com/fabikatchukoh/ar...ollab-804140653
There are a lot of work here, it will be useful for you.    

Incredibly, you obviously talent)

Lock your wrist. Use only shoulder and elbow.

Nice start bro. I'm not a pro but I'd like to share a few tips.

For drawing head/portrait, you might want to learn loomis method. Very basic but can be used for any type of head. There's plenty of tutorial on YouTube. With this method you can easily draw a face even by imagination (without reference)

For shading, I recommend you to start by practicing cross hatching techniques. Quick, easy to make correction and suitable for both pencil and pen. Once you get used to it, then it'll be much easier to learn blending method.