Unfortunately, in a year they'll also know that it's an old outfit. There are a number of components of classic style. You'll want to watch for them. For slacks usually straight legs are best. Avoid flares or tapers.
Cuffs go in and out of style.
It's best to avoid them. Pant legs for both men and women should go to the heel. Shirts and blouses should be of a conservative, classic cut. Again, look for moderate collars. Extreme collars are one of the first things that a fashion designer will change.