To plant miniature lily plants in pots or gardens, fill a pot with dry florists foam and glue a thin layer of dried sterilized soil on top of the foam. When the glue has dried, use tweezers to push the base of your lily stem into the pot. As lily stems are quite tall, your pot should be weighted down if made of plastic or resin. Stoneware pots work best to counter balance the height and weight of miniature lilies. Each lily stem grows from a single bulb so the stems almost always grow straight up from the ground and don't form a clump with multiple stems coming from the same point.
To plant them in a dolls house garden, I generally make a garden bed of florist's foam covered with dried sterilized soil, and plant the lilies in groups in the foam, arranging them to show off all of the flowers.
To arrange the lilies in a vase or container - Make your lilies without leaves down the stem length. Most florists strip off the majority of lily leaves in an arrangement. Set your lilies at the correct angle for the arrangement and insert the lilies into a bit of florists clay or modelling clay held in the neck of the vase. If you are making an arrangement in a glass vase, you can fill the vase with tiny clear no hole beads to represent the pebbles used in arrangements. Check that your vase will hold enough lily stems for your arrangement. The glass vase shown here has a narrow neck which will only permit the use of five lily stems. A larger arrangement can be worked into clay disguised on the top of the vase, but it may not look realistic. Always check your vase is suitable for your plans!