Determine a theme. Most all pageants have a theme and music and stage dressings that reflect that theme are the place to start when directing the opening number. Also consider the time frame of rehearsals. If you only have one or two brief rehearsals, it is not logical to think you can have an intricately choreographed dance number to start your pageant. If time and resources limit your rehearsals, stick to a parade of contestants, perhaps using upbeat thematic music where they dress to reflect your theme. Seeing the contestants in action while walking, speaking and modeling is the most important thing for both judges and audience.
Rehearse your opening number until the contestants feel confident. The opening number should really draw the audience in and engage them in the action of the pageant. In order to do this successfully, the contestants need to be confident with their movements and dance moves if applicable.
Pay attention to the traffic flow on stage. Even if you are only doing a very basic parade of contestants, you should make the traffic flow interesting. Have more than one column of girls entering the stage and allow them to move in such a way that shows their personality and interpretation of the theme of the pageant. This is the area of the competition to allow for individuality and express some creativity, so allow your staging to reflect that goal.
Prepare the contestants for introducing themselves. The opening number is the perfect time to have the contestants introduce themselves to the audience and the judges. Sometimes a catchy introduction makes a contestant particularly memorable, so encourage your participants to use creativity when preparing their introductions. Make sure you have microphones on stands that pick up a broad range and don't require height adjustments with each contestant.