Many distractions are under your control:

• they feel anonymous and uninvolved (can you involve them?)
• they're not all interested
• they have a limited attention span when they are interested
• they can only retain a small number of thoughts within a single "frame of awareness" (e.g. a viewgraph)
• they can't see your visual materials (do you have to use materials people can't see?)
• they missed/didn't understand a new term/concept (can you make sure they catch what's new? do you even know in advance what will be unfamiliar?)
• they can't keep up (why are you going so fast?)

Some distractions aren't controllable:

• they vary in experience and education (here you have to decide to whom you're speaking and do the best you can to take pity on the rest)
• they're distracted by their own thoughts (all you can do is be as animated as possible)
• they're uncomfortable: sore back or butt, sleepy, hungry, have to go to the bathroom, etc. (all you can do is take breaks and/or serve coffee and donuts -- but those strategies will play one distraction against another)
• none of us know everything; we don't even know everything there is to know about what we know

Rhetoric texts typically tell you to "know your audience." Here's what you need to know about them:

• their background and experience in your subject
• their point of view on the subject/level of acceptance of YOUR point of view
• their relationship(s) to you
• the extent of their sameness (e.g. land of origin, gender, economics, age, and familiarity with your jargon and style)
• their principles, relevant to the topic you present
• the risk associated with offending individuals
• the hope of the audience's receptivity

Generations

Your audience has generations: you present to the first generation, which repeats or passes on what they heard from you to the second generation, and so on. You can only directly control your presentation to the first generation of audience (and maybe the second). This is what makes companies use viewgraph forms with complete contact information on every page. The companies feel that as soon as you take a page out of context they no longer have any control of your understanding. Is this likely to affect your approach?

Whenever you try to make a point, you initiate the following process:

• You take a body of knowledge contained in your brain and model it. You have to condense and simplify this knowledge for the model to be of any use. How you simplify depends on
  • your perception of your audience,
  • your prioritizing of bits of information,
  • the complexity of the information,
  • your ability to retrieve it, and
  • how you feel.
• You communicate the model to an audience via words, symbols, images, numbers, equations, demonstrations, etc.
• The audience receives your communication.
• The audience reverse-engineers the communicated information to models of its own.
• Members of the audience merge their models with previous knowledge, experience, level of understanding, perception of context, and how they feel.

What will be the outcome? Just about any outcome is possible, depending on the size of the audience. Some of this process is completely uncontrollable. Consider:

• Information is sure to be lost between communication and reception under the best of conditions. Neither you nor the audience will know what is lost or when it happened, unless you can figure it out from the outcome.
• Even when you know your audience well, you are not likely to know specific members of the audience well, or to be able to address them specifically.
• You have to guess how well the audience understands what you're saying. And you have to guess before you say it.

You can't change the audience. And you can't control most of the process. All you can do is constrain those parts of the process over which you have control: the modeling and communication of information and the assessment of the audience. The writing and speaking are the tip of the iceberg. Your tools are

• the strength of your argument
• your confidence
• the depth and breadth of your knowledge and preparation
• your backup materials
• your ability to communicate what it is you want
• your recognition of other views, and of your own biases
• your credibility
• your ability to keep the audience focused
• your ability to find common ground

References

Korpela, J. "How all human communication fails, except by accident." http://www.hut.fi/u/jkorpela/wiio.html
Johnson, R., D. Johnson, and K. Smith. "Cooperative Learning: An Active Learning Strategy for the College Classroom." Baylor Educator, Winter 1990.