Advice from artists/painters/sculpters!!

Hello!! I'm a rising 8th grader and I decided after a LONG time that I'm going to a preforming arts high school, and majoring in visual arts!! I need to start beefing up my portfolio, my entry paper, and like reassuring my parents I'll be fine. I need art tips, especially on how to make works look 3d and how to make 3d works look good. And where you guys find inspo, bcuz our entries have to be original, no reference or tracing. And they accept beginners, I'm a pretty seasoned artist working on drawing with no reference or inspo. But it's honestly just easier to. I also just struggle with NO reference bcuz I suck at anatomy and shading. Any advice would be wonderful. THANK YOU GUYSSS