The moment of your presentation has arrived. Below you find some general advice for during your talk. 

Intended for: BSc, MSc, PhD

Buy your own pointer/clicker as soon as possible, it will improve your presentations massively. Because of the clicker, you are not glued to your laptop while presenting (or having to walk to it everytime you proceed a slide). Because of the laser pointer, you can actually indicate to the audience where they have to look at a slide if necessary. Most people use the Logitech R400 (I do as well), which connects through a USB dongle, and comes at ~30 euros. 

The first and very important advice. When you start talking while everybody is chatting, you are sure everyone will continue throughout. You came here to present, and the audience apparently came to listen. If they want to talk, they are totally free to go somewhere else. Simply signal you will start (you are introduced by the host, or you clap in your hands), and wait until everyone is silent. If they don't pay attention, you don't have to start. 

Once you start talking, make sure you look at your audience. Only looking at your screen is the quickest way to loose all attention. Simply look into the room, and continuously make brief eye-contact with different people, as if you explain that particular sentence to them. 

You will almost certainly talk to fast. You are nervous, you are enthusiastic, you have through so much about this topic, you simply. brought too many slides and are in a hurry (never do this). Your brain goes faster then your audience, to which everything is new, can comprehend. Is this you: remember to bring down your pace. We are not in a hurry here. 

This is the great added benefit of a clicker: you can move freely. 

Yes, you are here to speak to the audience, we understand. But that does not mean you need to fill every second of the next 20 minutes with your voice. Your brain needs a little break sometimes, and the brains of the audience need it even more. Therefore, sometimes simply take a few seconds break. The moment when you transition to a new Topic/Section (as indicated in the Contents slide) is a great moment to do this. Walk to a different standpoint, take a sip of water or a deep breath, look around your audience for 5-10 seconds. It may feel like ages to you, but your audience will love it. Their brain can recover briefly, and the atmosphere will not be so stressed/hurried. 

I already indicated this in the "Preparing Slides" section, but add questions to your audience at certain spots. Listening is a very passive activity, and at some point your audience will just zone out. The best way to keep their attention, to raise their adrenaline, is to actually activate their brain. Therefore, once in a while ask them a question about the material. Force them to think about something, and at least get back their attention. The question also helps them reflect whether they actually understood what you are saying. 

When you ask a question, let them think for 15-30 seconds, and ask for an answer. When nobody responds, simply wait a bit longer for an answer. You are not a solo clown that needs to entertain them: they are part of the game, and have a responsibility to participate. Usually someone will start to engage, and others will follow. 

This is also a surprisingly common mistake. Research shows you already lose attention of your audience after 10-20 minutes (that's why you need the questions and active engagement of the previous part). However, they are definitely gone after more than 45 minutes of continuous presentations. Therefore, you need to give them a break in time. Everything you tell after 45 minutes is just lost time. Note that, if you are properly looking into your audience (item 3), you can also tell from their faces whether they are still paying attention (looking at you). 

Sometimes you just brought too much material. You are extending to much beyond the assigned timeframe, and the moderator indicates this to you. The for example interrupt you, saying that you "need to round of in the interest of time". Or they signal with their hands that you have 1 minute left. Some people get super nervous in this situation, and think they still need to summarize every slide they have left. Never do this. This will take ages, and you will enter the nightmare where you are asked two, three or even four times to really really conclude now. Instead, simply apologize to your audience that you need to next slides, and go directly to your Conclusion slide. Summarize your take-home message, and accept that your time is up.