Ask questions, especially about records of previous decisions and jurisdictional issues. Align your testimony accordingly. Talk to others who have been before the agency to find out what the setting is, what to expect and what to avoid. Proponents often are treated more differentially than opponents and have the last rebuttal. The more you know the better but take care not to get hostile with opponents.
Time is extremely important.
If the notice of hearing says that documents must be filed by a certain date, there is rarely any room for negotiation. Testimony is usually timed. Find out how long you can talk. If you can not cover everything in three minutes, arrange to break the testimony into subtopics and have others cover the remaining points. Call the Clerk the day before to confirm the date and time of the hearing.