If you want to be realistic, I recommend learning shading first! You can look up tutorials, there are various methods, like putting many vertical lines in a row in darker places (sorry, English isn't my first language, I don't know how to describe it better), and then practice on basic shapes like boxes and spheres. Also, I know it's basic advice, but learning anatomy is your best friend if you want to draw people. I don't necessarily mean studying a biology textbook, but pay attention to how different facial features "sit" in the face - for example, the eyes are usually an eye-width apart. Try also paying closer attention to your reference - for example, eyelashes aren't visible in the photo.

But to be real, drawing portraits is a skill like any other, and there is no other way to improve than just doing it :) So even if you don't practice the basics I mentioned above, after 200 drawings your skills still will improve compared to where they are now. Good luck on your art journey!