The idea of a small wardrobe of pieces that work together is often called a capsule wardrobe. The term appeared in American publications in the 1940s, was revived by London boutique owner Susie Faux in the 1970s and popularised by designer Donna Karan in 1985 with her “7 Easy Pieces” collection.
Start with what you wear most
Outerwear, shoes, a handbag and well-cut trousers are used constantly, so quality shows quickly.
Think in cost per wear
Divide the price by the number of times you expect to wear a piece. A coat costing 400 pounds worn 100 times works out at 4 pounds per wear.
Choose versatile colours
Navy, black, grey, camel and white combine easily and reduce the number of pieces you need.
Check construction
Look at seams, linings, buttons and hardware. Pieces that are made well can be repaired and worn for years.
Source for the capsule wardrobe history: Wikipedia: Capsule wardrobe.