Inherently, the keynote environment has a built-in wall that must be recognized and dealt with. This wall is the one-way verbal information flow. Sure, there can be some two-way communication, but most of it is non-verbal cues from the audience. Normally, in a keynote environment the audience members do not have the opportunity, the desire, or the need to verbalize adjustments, suggestions, comments, questions, etc. to the speaker.
So, how can we capitalize on this dynamic? It involves a few pre-work items and mid-keynote items...
Learn the audience members' specific expectations for your keynote. What type of experience do they expect from your keynote, what do they expect to learn, etc.
Learn about the organization, association, company that the audience members represent.
Learn their language, their struggles, their successes, etc.
Start attacking the wall immediately from the start. Be yourself. Be authentic. Admit what you know and what you don't know. Connect with the audience through interaction, humor, entertainment, unique/interesting information, etc.
Keep the wall down by being clear with your purpose and bringing everything in your keynote back to that clear purpose. Keep things moving fast, but not faster than that particular audience can handle. Have a specific road map (points) you are following and let the audience where you've been, where you are, and where you are headed.