Know your audience - are they well versed in terminologies relevant to your topic, or should you use common
words
Know your purpose - You need to know what it is you're trying to do before you can do it.
Know your topic - If you don't know sufficient detail about your topic and rely on the audience having even less knowledge you aren't being effective
Follow through on what you say - Go into detail don't mention one thing and talk about something else
Communicate a little at a time - Giving lots of information can completely lose an audience if they can't take it at all. Breaking it down can help. Use multiple communication techniques
Present information in several ways - Perhaps showing images or using a presentation aswell as speaking
Develop a practical, useful way to get feedback - Question and Answer sessions (open forum) are a way to get feedback.
Use multiple communication techniques - hand gestures, talking, videos etc. are all different ways to get a message across