What activities can you use to settle the class as soon as they come in?
How can you give them all something to focus on, so that when everybody is there, and you're ready to begin, you can get on with the lesson?
NB. The context for this blog post is a situation where students turn up to the class in drips and drabs, maybe because they've just had PE, or they're coming from different parts of the school, or they've just had lunch, or whatever. (I don't want to get into a discussion about whether or not we should make students line up outside the class until they are all present and silent, as that is not what this post is about.)
The suggestions below are based on using a projector or interactive whiteboard (IWB), and they are examples of things that you can just put up on the screen and leave there, requiring no interaction with the board or your computer until you are ready to move on.