Your sketches are really good! And while I'm definitely not the most qualified to give advice, I think with the shorter timed sketches, it's best not to overthink where to put anything and to just jump right into putting down those first lines. With the longer timed ones, it's all about the smaller details to put into it. The hair, the fingers, the toes, the chin etc. and of course making sure the proportions are right, but your proportions look really good to me. Anyways like I said I'm not super qualified but these are just some things I think might help. Happy drawing!
