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Experiment with line weight a bit more; you're using very uniform lines a lot, and it's tending to flatten the image instead of creating depth. For example, the first portrait could benefit with thinner, lighter lines on the corner of the jaw and ear, which will help the depiction of depth and keep the emphasis on the face. Be careful not to frame the faces with the linework.

Yep. You will use that in certain instances, but for now it's better to develop different habits, so that when you place a heavy outline, you're doing it for a good reason. Think about that type of outlining as a visual aid, to lead the viewer to your subject or focal point. With a simple portrait, it's not necessary, unless you want them to focus on a particular part of it, like a locket or ear, that the viewer would normally skip over because their brain is hardwired to focus on the face.
Building a large crowd scene or something with a jumbled, busy background, a heavy outline could be called for; but even then, it will need to thin out in places, to keep the subject from becoming a flat, graphic image.

Ears.

Look at real ears.

Study them.

Know them.

Feel them.

Date them.

Draw way too many of them.

Another one.

Awww.. It seems like I have an addiction on critique; so bad that compliments give me an allergy. ^^;;;; Sorry, but I'm really a geek like that. Hearing critique on what I should do makes me wanna do better and gives me motivation to work harder; the slightest compliment however makes my backache worse, cuz then I ignore my ailment and attempt more drawings despite the pain. Doctors tell me I should stop doing compliments. XD

I'll try. crying