The Velvet Revolvers

[Jeso]

Love the idea, let's see if we can get this going :)

You've got some great studies for a start! I agree with bookend about the lack of dimension in the heads (though it's something I still struggle with myself), maybe also do some studies of the facial planes? Like this thing:
https://warosu.org/data/ic/img/0016/87/1...599047.jpg
And maybe some studies of lips, I noticed that you paint them very flat, and with very sharp outlines separating them from the face - they actually blend in a lot more (unless there's loads of lipstick on them, I guess).

I'm working on the very basics at the moment... drawing boxes. I struggle with the perspective quite a lot, anyone got any tips? I'm not even sure how to tell if these are correct - I only know that #99 is definitely wrong.

Whats up Oloriel! Welcome to the Velvet Revolvers, I can feel form those shapes you are drawing that its all out of whack. Because you are eyeballing the perspective? try using a Horizon line and vanishing points to get that perspective down to the T. Just like in the images Bookend posted.
If you have no idea how perspective works or its terminology, try watching some tutorials on youtube, just search for "Perspective tutorial" Im sure you'll find tons of info on the topic.