[Feedback] How To Improve My Audio Quality?

Hello, I recently really got into Voice Acting and I've been recording a lot of lines; but I'm wondering what I can do to further improve my audio quality? Like how is it?

So this is an example of my audio quality (go to the Undubtale and Tenth Line auditions): http://www.behindthevoiceactors.com/members/Kyotosomo/casting-call/auditions/

I record out of my closet (I made sure all walls are padded with clothes) and I use a basic Blue Snowball microphone which I have tissue like material laid over to act as a pop filter.

So as said, what can I do to improve sound quality? Like should I position the mic at an angle or keep it a specific distance away from me? Should I have the closet door closed with cloth on it or should I leave the door open (there will be an equal amount of silence regardless)? Any feedback would be much appreciated! thank you!