Brief details...

Max 20 Secs of Footage

Editing Properly - showing the skills and completing what you submit is more important than meeting the 20 secs.
You must demonstrate decent skills in:

LIGHTING
PERFORMANCE

It should be LIP SYNCED!!!

You must demonstrate TWO of the following FIVE (examples we showed you in brackets)

MULTISCREEN - you could either have many diff screens running at once (Benny Banks - Trouble) or perhaps on top of each other - layering - (Akala - Lose Myself)
GREENSCREEN - have a look at Erna, Sophie, Bariya and Tiffany's video from 2012-13 (13e5 Kate Nash - Foundations) to see how they used greenscreen - remember the cloth must be as smooth as possible when stretched on the frame
COLOURISATION - an effect put on in the editing suite - you can heighten colours or improve lighting (for example). (Little Mix - How ya doin' ft Missy Elliot or Benny Banks - Trouble)
For a video that needed the light and colour enhancing, see 'Lost' 13B4 - Tyra and Sophie (from 11-12 yr13 playlist on Coombe Media).
JUMP CUTTING - cutting MUST be on the beat exactly - expand the timeline in Premiere to see the audio waveforms so you can literally see where the beats occur - this happens in many videos - remember how will.i.am used the motif of a set of dancers to jump locations (will.i.am #thatpower ft Justin Beiber)
DISAPPEARING - with this, people or objects disappear or reappear. Remember using this effect relies on your having filmed the footage correctly - you must film the same scene 'bare', from exactly the same shot distance and position for it to work.