Two issues here. One would be the floor reflecting the sound, thereby adding a signal that is slightly delayed relative to the direct sound from the speaker. This is generally bad, so a rug IN FRONT of the speaker would help with that issue.
The other issue has to do with how the speaker should be coupled to the floor. Wooden floors that are suspended can act as a giant sounding board (generally bad), so it would make sense to decouple the speaker from the floor as much as possible to prevent this. With your hard ceramic floor, this is probably not a concern. Still, how the speaker sits on the floor will affect the degree to which the speaker cabinet itself will be vibrating and emitting sound. Some speakers are "tuned" so that the vibration is a good thing, while others are designed to be as free of such "extraneous" sound production as possible. The only way to tell what works best is to experiment.
With my speakers, what worked best was to absorb and dissipate cabinet vibration as much as possible. My speakers are big, floorstanding units. I removed the cones and placed the speaker flat on top of Symposium Svelte shelves (a 1-inch thick shelf with thin aluminum outer panels and a core of foam that dissipates vibrational energy as heat), with the shelves sitting in direct contact with a carpeted floor. The whole bottom surface area of the speaker is in contact with the shelf to maximize the transfer of energy. I've heard these shelves work well with a lot of speakers, but, favorable result cannot be predicted, one can only find out by experimenting.