There will be also a few tips for visiting the Dune all throughout this article.
Take a jacket. You are probably hot on the way up but quite windy at the top. Try the not so touristy part. The view is more impressive when it is only the forest, the dune, the sea and you on your own.
Take off your shoes. Walking on the soft sand is much easier and more comfortable without shoes. It also saves you the trouble of dumping the sand out of your shoes later on.
Try to avoid putting your bag on the sand, unless is properly sealed. Also, make sure there is nothing in your pocket before you sit on the sand, unless you want to spend the next couple weeks cleaning the sand in your wallet/mobile.
Run downhill, or roll down if you prefer, for this is the most fun part! It might look real steep and pretty scary from the top. But you can never fall because you every step will be deeply stuck in the sand. And even if you do fall, the dune will always catch you with more than enough cushioning.