Become familiar with how to use the AV equipment. Show how to use a peak flow meter, spacer or inhaler, if appropriate. If nothing else, put on your favorite teams baseball cap and mention how important it is to be a team player. That presentation took place years ago, but some people still mention it because I used unusual visuals to reinforce my message. Talk a little louder than you think you should.
Most people speak too softly and the result sounds like mumbling.
Projecting your voice and speaking slowly can also make you feel less nervous. If so, know how to use it. If you are questioning the effectiveness of the sound system, ask the individuals in the back of the room if they can hear you. Save handouts until after your presentation , if possible. If you give people materials at the beginning of your talk, they are likely to read them instead of paying attention to you.