I thought it could be helpful to someone, so here we GO =D
In principle I wash ALL my Lolita clothes in the washingmachine. And I don't distinguish between cotton, chiffon or velvet. Even dresses with prints are going into my washingmachine. I wash them at 40 °C (very rarely on 30 °C) with normal washing powder from the drug store or supermarket, because I want them to be deep cleaned. Some people will be screaming at me because they think that I ruin my clothes BUT there wasn't a dress that didn't survive it ;D
AND you have to notice that I wash with a german washingmachine, tap water and washing powder. On the labels are the recomondations for JAPANESE "washing conditions" so you have to figure out for yourself (if you live in a different country than germany or japan) what you can do to get your dresses clean.
There is only one exception: printed prints! There is a chance to melt the print away if you wash them with 30 - 40 °C. So it is best to hand wash them.
In order to wash your clothes more gently in the washingmachine you can also put them in a linen bag.
1. I try to cover the stain with Gallseife (following the instuctions) and wash them
2. If the Gallseife didn't work I try to figure out what stain it is and use special stain removers (Fleckenteufel, there are many types, like for gras or oil etc) and wash them (e.g. Dr. Beckmann Fleckenteufel for XY)
3. If there are still stains or colorations I use Klorix (some kind of bleach you can also use to disinfect something). I give a small amount to the washing cycle (after 10 minutes or so, when the clothes are drenched with water). The worst case with the bleaching you can get is that the stain is still there or the colors aren't that vibrant anymore (but not thaaaaat much).