I heard this ages ago and have had a hard time verifying it, but rumor has it that J. Crew employees are always encouraged to wear five pieces, which is apparently a magic layering formula to look put-together and J. Crew-y. 

My Style Icon, Jenna Lyons

Look at Jenna Lyons on the left: tee + cardigan + blazer + belt + skirt = five pieces.

(I think this formula describes what you wear on the main part of the body and doesn’t include shoes).

While not quite hitting the five mark, I also liked this sleeveless sweater over long-sleeved shirt with jacket look from In Style:

And finally, a few tips on How to Look J. Crew: 

• Wear just one piece of bright clothing (or an accessory) against a backdrop of neutrals. J. Crew often showcases neon pieces this way. I particularly like light gray as a canvas.
• Consider these building blocks as your J. Crew wardrobe staples: 
  • Light sweaters or cardigans, button-down shirts, V-neck tees, simple leather flip-flops, bright ballet flats, printed heels, a schoolboy blazer and a classic wool winter coat in a bright color.
• Mix smart pieces with casual items. 
• Cuff your sleeves the J. Crew way.
• Don’t be afraid to combine prints, especially stripes + anything else.