Although you wouldn't stumble upon it unknowingly, the beach is not hard to find, and you probably won't have it to yourself unless you go at sunrise (shown above) since its location is even on Google maps (search for Red Sand Beach Hana). The beach itself is public, however you technically have to cross through a small strip of land owned by Hana Ranch to access it (unless you have a boat). This is not a big deal in reality since so many people do it, including locals, but make sure you show respect and stay on the footpath. DO NOT blaze your own trail and DO NOT act like you own the place.
Once you arrive in Hana, take the first left after you pass the Travaasa Hana Hotel. This will take you to a T-intersection in front of a community center. Make a right, and park anywhere on the side of the street. To the right of the community center, you will see yellow gates. Walk through them and head towards the coast, where you will see a series of trails. Just pick one and follow it to the ocean, then hike left along the (beautiful) coast for 5-10 minutes.
Take your time as it can be steep and slippery at certain points, but it's totally worth the walk. We were fine doing it in flip flops, although the unsure and unathletic might want to consider sneakers.
[Photo: Will McGough for Jaunted]