A basic skirt0
One of the staples of the Lolita wardrobe is an above-the-knee length skirt with petticoats.
The first image is from Mary Magdalene and the second is from Moi Meme Moitie (Mana's brand). I think both of these are gorgeous.
You can make a simple skirt using a circle skirt pattern, or easily create one with your own measurements. It takes a little bit of maths but its not too hard.
You do need to remember that because its such a full skirt it will need quite a lot of fabric and trimmings. The skirt pictured has a 5 metre hemline - which means it needs 5 metres of lace to go round the bottom.