As with any dry cleaning, there are things you can do to assist the successful cleaning of your dry clean only garments.
Let the professionals do the work. Don't try to remove stains yourself. Some home stain removers cause problems that can't be reversed.
Be honest. Point out the stains when your dropping of the garments and identify what caused the stain and how long it has been there.
Make special requests up front. If you have concerns about loose buttons or small holes, ask the cleaner to check them or make repairs. If the garment is vintage, share that as well so it can be treated even more delicately.