I have seen many people with avatars that are supposed to be their minecraft skin's face but in the end just look like a blurry mess. I also could not find too much explaining how to do this so, I have made this tutorial!
You will need GIMP and that is all, along with your skin of course.
1.) Open gimp
2.) Use the select tool and select the face
3.) Next go to Image> Crop to selection
4.) You should now have a crop of just your skin's face
5.) Now go to Image> Scale Image...
6.) Make sure you have interpolation on none and the chain looks linked together (this makes it so it keeps the ratio when it scales)
7.) Select the desired dimensions and click scale
8.) Go to File>Export...
9.) If you export as PNG it should bring up another window, just press export again and your face is complete
I hope this helped you out!
Also, I could not find a section that covered graphical tutorials, or anything along this range so I put it in this section.