When you present you are in charge so make sure the environment is how you’d like it to be. Most speakers don’t realise this and consequently presentations are not as good as they might be. The lighting, the position on stage, the temperature, the surroundings, the room, the volume, the screen, the time and even the audience may all be altered by the speaker to their advantage.
Consider yourself how, as part of the audience, there are factors in the environment that have limited the effectiveness of a presentation you have received. All of those factors are amenable to change and with appropriate timing alterations can be made. Clearly all this depends on the specifics of your presentation but try before you speak to be part of your own audience. 
Consider the environment. Can you see the speaker? What is the effect of the lighting set up? Are there windows or lights that alter your view? Is there unnecessary clutter in the room such as flipcharts, extraneous equipment, stray chairs, monitors? Is the set up of the room ideal, not just acceptable but ideal? How long have the audience been sat there? Would they value change in position or a quick comfort break? Make changes and make it better.
All of these issues noted above can be altered by a speaker simply by asking. It may take a little time to find the appropriate people to help but support staff (or just friends) can make dramatic changes often with minimal fuss given the time and request. The lighting can be improved, usually by turning it up, not down. Blinds can be drawn to block light from behind a speaker or the position of the speaker altered. Clutter can be removed, tables can be rotated or even the whole room altered, if you take the time. Did the previous 3 speakers over run? Then offer the audience 2 minutes just to chat or to stand up and sit down again. It needn’t be cheesy but such positive interaction endears the speaker even before beginning.
Many speakers don’t believe they have the “authority” but actually yours is the complete privilege and authority. Make the environment as good as you can for your audience; they will repay you heavily. Your presentation will be better received.