Something I make all my students do.
Come up with a 5 minute showcase of all your best talents and memorize it until you can play it with your eyes closed.
Combine several different techniques from strumming some complex chords, to lead and pull/off, hammer/on tricks, segway into some fingerpicking and then move into some tapping and two handed piano chords. Make everything gel together and improve on your showcase over the years as you get better.
Then when somebody says 'play something for me' or you get stuck in a contest, you'll always have something prepared. The secret is in variety and doing things that look difficult and impressive to not only guitar players but those in the audience who are impressed with fancy finger movements.

Try to be the last person to perform and once you've finished... pump your fist in the air with a big smile on your face and even if you screwed up... make it look like you did the most amazing solo ever done...
The audience will go nuts and even the ones who are tone deaf will assume you've done something incredible because you look so excited about what you played.

Wear cool clothing and use a Marshall stack so you look like a rocker.
Long hair doesn't hurt either, but a fast tapping solo will beat out just about anybody.

The other secret is to have a ton of friends in the audience. Most of this contest stuff is judged by audience applause.
You can win one of these things even if you aren't the best, just by bringing 30 loud friends along.