Another trick you can use if you're stuck with fixed seating is to ask the audience to choose a new seat after they come back from a break. For example, tell them that part of the reason to come to a speech is to meet and interact with new people and by changing seats this goal will be accomplished easier. Another thing to watch out for is a situation where seating arrangements in an organization have been established over a long period of time. When possible set the presentation to the long side of the room so the last row is as close to the speaker as possible. Avoid long narrow rooms which put audience members far from the speech as if they were in bowling alley.
People prefer to sit by aisles.
Avoid chairs next to walls. Audience members will feel trapped. Aisles should get bigger as they get nearer the exits because they must accommodate more people. Make people sit as close as possible to the front. Force them to front with reserved signs on back tables or keep chairs stacked until all front rows are full.