Dude, without looking at the title, your thumbnail totally looks like Voldyshorts, so that right there means you have potential. Now, you're probably tired of that, because EVERY artist, friend, on-looker, teacher, enemy and pet snail will tell you that 'you have potential.' But, fear not, because you actually do. I'm betting that if you have one hundred harry potter fans look at this, Ninty eight of them would be able to tell you who it is. (Don't ask non-fans, they are hopeless)
Before I go on, I was wondering, did you use a reference image? Because that would be my number one suggestion.
Number Two is that one of the biggest and most important parts of portraits is proportion and spacing. Grids are a great way to make sure your eyes aren't to close and your mouth isn't to low in your drawing. No matter what anyone says, 'There is NO wrong way to draw, and nothing wrong with grids.' Some of the best artists use them. (I can send you to some if you don't believe me.) [And if you need help with grids, you can note me]
Now, everyone also says, 'draw what you see, not what you Think you see.' That is true too. You'd be surprised what walking around and drawing rand00m objects and body parts can do for you drawing skill. Just draw lots of different things that you would think are 'To hard.' Look at them differently. Just draw.
For teeth, Try not making such a dark outline. This will help you avoid an overly cartoony appearance.
Lastly, shading will do a great deal to make a peice look realistic. It especially makes odd, flat things and wrinkles easier to draw.
So, overall, Brava for lord voldy and your drawing. I can see you becoming even more skilled in the time to come. If there is anything I can help you with, just note me and I will do my best to assist you. Keep drawing and getting even better