I've done a couple LW posts on speaking skills (none intended to be Dark Arts-y), in case you find any helpful:

Four Tips for Public Speaking - The four tips that seemed to improve speeches the most, fastest, when I was mentoring other speakers in college

False Friends and Tone Policing - Ways to recognize if you're giving inadvertent offense that is making it impossible for your audience to listen to you

Change Contexts to Improve Arguments - Putting thought into choosing good environments for disagreement (my living room, with freshly baked cookies, makes people feel safer and more inclined to engage with ugh fields, than rapid-fire and in public on facebook)