Liven up story time by instructing the children to act out what you read. Dress the children up a little, too -- if you're doing the story of Little Red Riding Hood, for instance, one preschooler would wear a wolf mask made in a previous lesson and another would wear a red coat with a hood. Make sure to alternate the children for each story so all the preschoolers get to have a go.
Don't confine dramatic play to the classroom; dress the children up and send them outdoors. One good outdoor game is to have all the children stand next to an adult at one end of the yard. The adult yells a type of animal or mode of transportation before saying "how did you get there?" For example, "Airplane, how did you get there?" The adult at the other end of the yard answers, "I flew." This is the cue for all the children to pretend to fly to the other end of the yard. This game continues back and forth, with the children hopping like kangaroos, stomping like elephants, or whatever you can think of.
Oven mitts that look like animals can make good hand puppets. They can help to bring out the confidence in shy children. Those who would normally not contribute in dramatic play are more likely to do so when talking through their puppet.
Get the children to draw lots of faces of different animals, roughly as large as a child's face, and then cut them out, as well as holes where the eyes should be. One child will close his eyes while the mask is put on him. The other children will then give clues as to what he is until the child guesses correctly. These clues can be whatever the children like: for a pig a child might say, "You have a snout," make an "oink" sound or even pretend to be a pig. Ensure each preschooler has a turn.
This is a little more ambitious than the previous ideas, but a fun way to bring summertime into the room no matter what the weather or time of year. Ask all the preschoolers to come dressed in swimsuits and sunglasses and fill the room with beach towels and beach balls, as well as a paddling pool with enough water for the children to get their feet wet. Make sure the area around the pool is surrounded by towels in case of any spillage.