GIG's Art and Music Potpourri

[Evil Yoshi Toes]

Nice drawings. To make the faces look less flat watch the shadows. The reason they are looking flat is because the shadows are not showing form so having them isn't doing much for your characters. You should look at how shadows fall on a real face with the lighting you are using.

Spoiler

The light is coming from the right on this photo. Watch how the shadows wrap around the forms of her face. The nose casts a longer shadow where it protrudes most (the tip). Your light source isn't as strong so it the shadows will be less dramatic, but the same knowledge applies.

Spoiler

Looking at charts like the one above can also help sometimes, but for me the most helpful way of figuring out lighting is to just apply the lighting to myself with a lamp and taking a photo.
Your style is very simple so you'd have to simplify the shadows, but you should still take into account the way shadows work in real life and manipulate it into your own style. You also have to consider the structure of each face, for example someone with pronounced cheekbones will have more of a shadow underneath (with standard top 45° lighting). In the end it comes down to observing real life and applying it to your own style.

On the subject of observing real life, I'd watch your anatomy especially when it comes to shoulders and necks. In the drawing of the girl's face, her neck is thicker at the top and tapers as it goes down to the chest, which is the opposite of what a neck should do. Her chest is also very high up.

The drawings are nice, just keep drawing and observing real life and you are sure to improve