Giving a talk?
Don't let the tech take you by surprise.
Figure out beforehand: what kind of mic is it, should I bring my own clicker, can I just plug in my laptop, what is my backup plan? Be prepared - it helps with the nerves and gives you confidence.
Generally speaking*, avoid standing behind things.
Desks, computers, lecterns, we want to connect with audiences and having a literal barrier between you and them hampers that connection.
*There are exeptions to every 'rule'