Because fashion, fame and celebrity go together, make your runway show have a Hollywood theme. The backdrop where the models emerge is a perfect place to replicate the iconic Hollywood sign. Make the runway a movie premier red carpet or line the walkway with giant, gold stars like the Hollywood walk of fame. While there are likely to be people taking photos of the models, add some extra flashes of light to enhance the celebrity feel of the event.
For a more urban and grungy look, recreate a city sidewalk complete with flickering street lights, brick walls with graffiti and overflowing trash cans. For sound effects, use police sirens, arguing tenants and squealing tires. Dress up the runway to look like a cracked, cement sidewalk or a curb and gutter complete with parking meters and a stop sign at the end of the runway. Add in a blackout and shine a overhead spotlight with helicopter sound effects.
While a forest scene might not fit if the styles are sophisticated or elegant, outdoor wear and animal prints are a great fit for a woodsy theme. Add some drama by including trap doors in the runway floor. Some models can climb in and out of the floor instead of through the typical entrance. Overhanging branches, moss covered rocks and outdoor sound effects will add to the overall environment.
Perhaps best for a child or teen fashion show, you could decorate the walkway like the spaces on a game board. Giant dice, over-sized storybook pages and huge toy cars would make for a fun decorations on the runway and stage. To keep the theme from being too youthful, use some rock music or age-appropriate rap music. Instead of everyone wearing fashions, have a few models costumed in game pieces like the top hat from Monopoly or a knight from chess.