Hanging lights on branches. Go natural with a fat branch and hang a combination of ornaments and candles attached with wire. Use twine or strong fishing wire to suspend the branch from above. You might want to try hangers so as not to damage your ceiling.
Floating Flower Tip - Most flowers float pretty well on their own until they start to pool with water and slowly sink. For a longer lasting centerpiece, use bubble wrap to make little skirts for your flowers.