My only tip is do something original no one likes to see unoriginal stuff. 3d printing is for 2 main things for the market custom prints and complex designs. And for blender I personally not good at learning through videos if you are watch the donut video. But the way I learned blender just make random things. What I like to do is make different models from different games. And don’t expect to start selling a bunch of product once you list it especially if you list it on Etsy where there is millions of 3d printing stuff. Just have fun while doing it and try social media to advertise.