Thank you guys for the comments. I think on the next one, I'm going to try a modified circle skirt to get the bottom more full.
The bottom hem needs to be roughly 3x the size of the person's waist. On brand name Lolita skirts/dresses, that's typically around 85-90in circumference (not including a ruffle). But-- while a circle skirt might give you the right fullness at the bottom, it doesn't give the right shape over a petticoat for Lolita.
The best way to get that fullness and
the right shape is to use a rectangle pattern (Just go straight across the whole width of standard 44in wide cotton, and you've got it), stitch up the sides, then gather it down. You can also do really full princess seams, but either way you want something really cupcakey. The standard length is also knee length, which is normally ~21in long.
I suggest browsing LolitaFashion.org
for information if you're interested, and I suggest browsing Lolita brand websites for good ideas about the right shape/silhouette. (Links available on the website mentioned. To make it easier, though, some of the best examples: Mary Magdalene
, Victorian Maiden
, Innocent World
, Moi meme Moitie
, Baby the Stars Shine Bright