Scarlett Johansson jokingly says:

The secret to looking good is to keep a makeup artist with you all day long."

But the actress is serious about the pressure to look polished all the time!:

...On the red carpet, I want my skin to glow and look perfect."

Her one secret?  Suncreen, of course!:

I come from the sunblock generation, so I've never been one to cover myself in oil and sit out.  I do try to get a little color when I'm on vacation, but I always wear day cream with SPF.  [Her choice? Jurlique Purely Age-Defying Day Cream SPF 15 ($45 at Amazon)]  I try not to moisturize too much in general, though, because I find that my skin balances itself naturally."

Her other must--her famed red lips--are kept perfectly crimson by employing a handy make-up trick:

If you plan to be out all night or eating dinner, bring a lip pencil with you to reshape and color in your lips, then throw a gloss on top.  Otherwise, if you try to reapply lipstick in a dark bathroom, the shape just gets weirder and weirder."

(Wenn)