You don't have to flout the fingertip rule quite so aggressively, but do look for the three Ss when shopping for a non-granny-ish skirt suit: short(er), slim, and soigné (AKA elegant, not tacky). And velvet Saint Laurent is always a good idea.
An almost-HTT (head-to-toe) print can be full-on, but 1) it's definitely not Melanie Griffith's '80s power suit, that's for sure, and 2) it makes you seem taller. When you're browsing the high street—Topshop especially is making an effort to produce fun matching sets—remember this Gucci ensemble's not-stiff skirt and cropped jacket. A shortened torso and relaxed bottom half can make even a grownup costume feel fresh.