I've made several miniatures, I think my favorite was a dollhouse quilt. The whole finished quilt was 5 inches and had 4 basket blocks in it, plus borders. I also made a feathered star, I think it finished at 5 or 6 inches, it was pretty challenging.
My tip is to paper-piece it, but instead of stitching through the paper, fold on the line and stitch right next to the line. Also, use a fine 60 wt thread like Bottom Line. It will take up less room in your seam.