When presenting, arrive early to setup, test connections, and make sure everything is ready.
I have attended a variety of professional concert events including the rock group KISS, contemporary Christian artist Amy Grant, the legendary island man Jimmy Buffet, Seventies crooner Neil Diamond, and numerous classical concerts. For all of these events and many others, I never saw the band or orchestra doing a sound check while we were trying to find our seats. Instead of waiting until just before show time to make final tweaks and adjustments, professional musicians have learned that it is more beneficial to arrive early before the audience arrives.
You, as a presenter, can apply the same practice to your presentation. A number of technical gremlins can cause delays and problems. Being present early enough to check and correct audio, visual, and computer connections will mean you are ready to present when your audience arrives. Additionally, by working through the technical and setup details in advance, you can utilize the time just before your presentation to find a place to mentally prepare or spend time speaking with audience members.
Beyond the preparation to ensure that all of the logistics, presentation slides, and technical adjustments have been made, it simply looks professional to be prepared and ready. In Britain, at least when I was a there as a child, the trains run on time. If a train is scheduled to leave at 8:03AM, you'd better be on the train by 8:02AM or you may miss it. This is sensible as there is a network of trains waiting to move in to the station and there are other trains people have to transfer to along the way.
As much as possible, I try to start presentations or conference calls on time – i.e., at the announced start time. Will some people be late? Yes. But some will be there early. It is professional to start on time. The likelihood of this occurring is enhanced when you arrive early enough to test your presentation, Internet connections, and other logistics.