Hello, people of the internet!
Last night I was just surfing the interwebs (as you do) and I fell into a black Pinterest filled hole surrounding the iconic hair of the Olsen twins. Their classic waves have become the staple of their look by being beachy, relaxed and natural to suit any event. My hair is a little too short to pull off the exact look off but I've still tried the different techniques suggested below and was very happy with the result of the "bed head" turned "fashionista" look that accumulated.
There are three different ways of accomplishing this look. The first involves wet hair. Start with about 30-50% dry hair and scrunch in some hair mousse throughout. Let self-dry and if your hair is naturally straight, spray in some salt spray for extra texture. If your hair is really unwilling to cooperate, braid into a plait while it dries. If you want to go the extra mile: once your hair is dry, use a straightening iron and create bends and kinks in the hair for a natural wave.
The second option also starts with semi-dry hair so start by blow-drying your hair with the aid of a round brush (pick a size depending on your hair length- small for short hair, large for long hair). As soon as this is done, twist your hair up into a bun (or maybe two - three if you have thick /long hair- depending on how tight you want the curl to be). This is because your hair will set when it cools down after the blow-dry and the bun creates more uneven waves than an iron would. Once about 10 minutes have passed, take your hair out and spray with some hairspray and dry shampoo for volume and durability.
Start with dry hair and use either a large barrel or double barrel curling iron for loose waves. Make sure to curl in different directions for different amounts of time in different size pieces. The key is variation for that "natural" curl. Tease the hair near the roots and throughout to loosen up curls while adding volume and add some hair spray. Finally, add some hair oil to the ends to seal the tips of the hair and create shine.