Lift your cup up gently a small distance from your work surface to check that the cup is bonded well enough to your saucer. The bond should be strong enough to allow for any items you will add to your miniature scene in the saucer. If you plan on using a lot of metal miniatures as accents, you will need a stronger join than if you are using foam and paper for your landscaping. Neaten the glue or sticky clay joins so that they show as little as possible, while holding the saucer and cup firmly together. Florist's sticky clay is often used underwater to hold metal floral frogs to glass containers, it will support a surprising amount of weight without giving way.
If you wish a more permanent bond, use two part epoxy glue.