A big part of line quality is confidence, which is built over time with lots and lot of practice. Keep drawing every day! If you find that you draw fast and messy, you could try slowing yourself down by spending time thinking about the purpose of each line that you put on the paper. If you're not used to working this way it may feel unnatural, but with time and practice you will speed up and do this process intuitively. Good luck :)

I think my only feedback is on the hand, it feels like you were focusing a bit too much on the smaller details of the hand, like at the area near the index and thumb. I struggled a lot with the hand too lol, focusing too much on individual little details/lines instead of communicating the shape. Overall these look like solid attempts, I like your penguin it turned out nicely.