Generally, knee-high lace-up boots are the most accepted. Often you can buy them with bows, scallops, and other cute decorations on them, but plain ones that have a more delicate shape (so not Docs or some other really clompy style) work just as well. Some people also really like "granny" boots, those lower calf-mid calf fairly plain ones. If you have a creative coordination, you can get away with all sorts of boots -- Uggs, wellies, etc. I wear regular "fashion" boots with loli all the time, but generally as an everyday kind of thing because the ones I have are really comfy to walk in. I also have some really short tan-coloured lace-up boots that I love, but they are a little more out there (especially with their ~3.5" heel, haha). You also don't want fetish boots or anything too sexy.
If you are just starting out, it is probably best to stick with regular knee-high lace-up boots. this
would be a good example Note the delicate shape, feminine detailing, and relatively sleek shape (though platform boots in a similar style are also acceptable).