FInal product is exactly 1920x1080. Make sure you record wider than that at a 16x9 ratio. Use Background image to the right for proper Ratios (Don't stretch it or modify the ratio).
Under 2 minutes
Every Second past that is eating into peoples patience.
Create Movement
Zoom in on things (easy on iphone or ipad recordings)
Music, Always
Even Cheesy Music keeps it interesting and sticky/memorable