Summarize:

Being outside for the day often means tanning (voluntarily or involuntarily) so showing skin has become not only socially acceptable, but actually encouraged.  Crop tops, cut-offs, cutouts, bathing suits, bandeaus and  bustiers are all popular. Outdoor festivals are almost always in the thick of summer, when it is hot and sunny. Always bring and wear sunscreen religiously. You don't want to get sunburned. Prepare for rain. Always remember to bring a poncho or rain jacket to avoid being soaked all day. If you are revealing a large amount of skin on top or bottom, even out it out with a more conservative counter-part.  Pair a cropped top with a maxi skirt, or cut-offs with a baggy button-up. Using a "flowing" top or bottom creates a chic look without looking too conservative. Loose flowing components to your clothes will be more comfortable in hot weather. Try a one piece instead. Rompers, dresses, and jumpsuits are very popular music festival choices. This "balances" your outfit for you since most designers dance on the "conservative" and "revealing" line. Patterned one-pieces add depth to an outfit. Floral patterns, abstract patterns and animal prints play into the indie look. Sandals or flip flops are fashionable summer footwear.  The important thing is to play into the summer look (gladiator sandals, chunky heel or jeweled flip flops). You can also look chic in something more structured (loafers, boots, or high fashion sneakers). Keep in mind that if it rains it will be muddy. Plan to bring several changes of shoes, including a pair or sneakers for wet days. You should choose accessories that complement your outfit and hot sunny weather.  Big floppy hats and over-sized or wafer sunglasses will help you protect yourself from the sun. Scarves, cross side bags, dangling earrings, and layered necklaces also pull together the look. Natural or neutral accessories are best. Wear your hair down, pulled back in a curled ponytail, in a messy bun, or up in a cute braid. Make-up should be minimal and natural. Make sure you wear sunblock to protect your skin from the sun.
Choose a casual outfit that shows some skin. Balance out your outfit. Complete the look with the right shoes. Throw on some accessories. Keep your hair and makeup styles minimal.