Be calm and witty even in the most sweat-inducing situation.
When your child is throwing a tantrum in public, calmly smile at the strangers staring open-mouthed at you and tell them "This is nothing. You should see my meltdown!"
Look ridiculously good.
Wear pretty shoes. Because if you're wearing nice shoes, or say, sandals that show off a pedicure, you MUST be an uber cool mum who, despite all those kids hanging around your neck, still finds the time to be glamorous.
Create picture-perfect moments and send them to everyone you know.
Get your kids dressed up and take them to the park, then snap them smiling and frolicking (spontaneously, of course!) in the autumn leaves. Then post the pictures on Facebook / put them in holiday cards / frame them.
Pretend to be super-organized. (unless you ARE organized, in which case, no need to pretend.)
Organize your bag so that, when you need emergency supplies in a pinch, you can pull them out oh so cooly. Which is much more elegant than foraging through your massive bag for five minutes, finding nothing but a crusty old sock and a half-eaten brownie. Everyone will think you're extremely organized.
Create an illusion of neatness in your home.
Attack your cluttered entryway with spears and daggers. No wait, with the feather duster. Arrange the mishmash of shoes, coats, scarves and hats into storage boxes, racks and hooks. That way, when people first walk into your house, they'll be wowed and impressed by your neatness.
Be ready with a last ditch attempt to pretend everything's FINE.
Take a comb with you when you go out so that if all else fails, everyone can still have tidy hair.