For quieting the two's and three's use a mouse puppet. Explain to the children when they see the mouse puppet held up it's time to be as quiet as a mouse and they only say what the mouse does. When the classroom is getting noisy and you want it quiet just hold up the mouse puppet. It usually works, sometimes you may have to tap the puppet on there shoulder for them to see, but once they see the mouse they get quiet.
I have a big rug in the middle of my classroom. When I want to change what we are doing, I ask the children to go sit on the rug. Once on the rug then it is a lot easy to line the children up because they are all together.
When transitioning from one room to another in our center with toddlers, I ask them what their favorite animal is. With their responses I then ask them to walk like that animal to our destination.
To ease transition in to the classroom, I always ask parents to give me a few family pictures of them and their child with other family members. I arrange them on a background the child has created (usually a finger-painting) and laminate. I place it at the child's eye level near where the child will rest for naptime. As they drift off to sleep, or are feeling a little sad, they are soothed by looking at pictures of loved ones!