The GM's attitude makes a huge difference in the players' style. Make efforts to draw them out, encouraging detailed descriptions of their activity. Remember, they have as much stake in the game as you do: Incorporate their descriptions of the environment into yours. If someone says "I swarm atop the table, then leap forward, grabbing the chandelier and swinging forward to deliver a powerful flying kick to the enemy sergeant!" don't be the guy who responds "Actually, this area is lit by candles on wall sconces, so you can't. Additionally, such an attack has a -4 improvised weapon penalty and your foe gets an attack of opporunity."
This doesn't mean that you encourage munchkins trying to unfairly seek advantage, instead rewarding cool play by eliminating penalties that might otherwise shut it down. If they don't serve to make things work better, toss 'em! If your PCs start abusing their newfound freedom, shut them down. "I may have said you could use frozen fish as boomerangs, but the supply of ideally curved fish has dwindled."
Additionally, concrete rewards make it easy to motivate your players toward more cinematic play. Give each player some tokens they can use to reward the other players for cool descriptions and heroic roleplay. Keep a few yourself, and let the players know they can only use the tokens given them by others, not the ones they started with. These tokens might represent extra "action points", bonuses to die rolls, free rerolls, or other minor benefits.