Presentations are a really good way to get all the jammers together in one place.
One of the requirements of Global Game Jam is that all the jammers are shown the keynote presentation at the beginning of the event.
GGJ Opening Keynote
If your internet connection is not too good, then the keynote and subtitles will also be provided as a download file. You can download this in advance of the event.
Make sure you have a good sound system and that all the jammers can hear.
Make sure you turn subtitles on in your language on the Keynote
//TODO add instructions
You may also want to consider writing up your own slides before this presentation. //Link to a template?
Closing presentations are a really great way to bring all the jammers togerther at the end of the event, and share what has been made during the experience.
If you have a large site with many teams, then a good way to do this is to ask the teams to produce a 2-3 minute vidoe of gameplay which they can talk over. This keeps the presetations short and concice, and minimises technical issues. The vidoes can also be uploaded on the project pages of GGJ website! If already uploaded to YouTube, all the vidoes can be made into a playlist, and played through one computer (meaning no need for annoying HDMI converters or projector techincal problems).
Other things to consider
If you have hearing impaired jammers, consider trying to find a sign language interpreter for the presentations.