Intro

I've been an Audio Engineer for 8 years and I've worked a lot of conferences where people have no idea how to use a microphone.

Recently I've found a paper that Gwern linked to provide credibility on why it is that presenters should have the basics of microphones and other presentation technology down. That is, if you care about the impression your audience will have from your speech.

From the abstract, "people evaluated the research and researcher less favorably when the audio quality was low, suggesting that audio quality can influence impressions of science." I will say, even if this isn't correct, imagine the mindset of an attendee where if they're even slightly interested in this topic but having difficulty understanding or hearing you. Some line of interrupting thought will arise saying, "I wish they would turn up the voice" which distracts from your transmission.

While working for these different companies, it'd be difficult to tell the clients that something they could do would improve the situation. Generally, the people that are paying you want a solution that allows them not to think about it, "do whatever you need to take care of it."

Fortunately for me, I don't work for any of you and can express the thoughts of my experiences:

If you had issues with sound, it's pretty likely that it was your fault*.

*obviously this isn't true in every case, but it's been true enough that I can make jokes with most sound engineers I've never met on how presenters use mics and it acts as a shibboleth of "I understand your pain."

So, how do I improve?

1. Hold the mic close to your mouth.

Basically, I can turn down your voice if it's too loud, but turning it up causes a lot of problems. In this case, having too much is much better than not having enough. It also sounds better if you do this. 

Here's a cool pic:

2. KEEP holding the mic close to your mouth

Yeah, see point 1.

This guy started with the mic close, then started to lower it. Look what happened 

3. Point the mic at your mouth

Even the general direction is fine, just imagine holding a flashlight and someone wants to see inside your mouth. There's an angle that the mics work best with, and this will probably be the best for the mics you'll be using.

"What if it's actually not my fault?"

Yeah, fair point. To start off, it wouldn't surprise me if most of the places you'll be speaking at have a big cost on hiring A/V people and that's because if people are good then they need to get paid well to keep them around. Especially for a field that has pretty terrible schooling options or even an "unofficial" training methodology, if companies find someone who is skilled that company should be paying them well (and you can do the well trained a favor by giving compliments to their manager. If you didn't notice anything and your presentation was easy, that deserves a compliment.)

But yeah, sometimes companies may need to train someone on the job. If that's the case and something goes terribly wrong, do not freak out at them. Having a patient, friendly smile and asking, "what is it we can do to resolve this?" will get the focus back to problem solving instead of, "everyone knows I've made a mistake and now I need to figure it out in front of everyone." With you on their side, it makes your presentation more likely to succeed.

If you're in the middle of your presentation and something starts going wrong without them being able to remedy, then there may be limited help at that point and try to do the best you can. The next best option is if you have a designated volunteer, get their attention and they should have an on-site contact they can get a hold of.

Not to panic though.This is pretty unlikely to be irreparable and slight hiccups happen but in the mind of attendees aren't registered highly. They're here to see you :) Absolute worst case (if things are REALLY bad), your company should talk to get some refund as the peace of mind is what you're paying for.

Closing

That's it! I hope this advice is helpful and if there are any questions I can help with feel free to contact me. Best of luck!