Check the care tag, first and foremost. While there are some linen textiles that don't require dry cleaning, many linens do. A dress that needs dry cleaning after every wear can become an expensive proposition. Look for machine-washable linen textiles rather than dry clean-only fabrics if easy maintenance is a must.
Purchase a linen dress that has a lining. Not only will this mitigate damage from sweat stains and other environmental products, but it will also ensure the dress drapes and hangs better on the body. A lined dress will also last through more seasons of wear than an unlined garment.
Look for softened or pre-washed linen to avoid getting a scratchy garment. Raw linen fabric is often abrasive to the touch, so look for words that describe the fabric if you're unable to touch the garment itself. Otherwise, always feel the fabric to make sure it's something you can stand to have near your skin.
Get a dress white or natural colored and stick to dry cleaning only. A brightly colored linen dress will lose dye over time and fade, much like a pair of denim jeans.