The first thing to do on Molokai is to drive everywhere. It’s a feat you can accomplish comfortably in two days. Depending on where you stay, spend one day exploring the west end and the other day exploring the east end. Basically you have one 40-mile west–east highway (two lanes, no stoplights) with three side trips: the nearly deserted little west-end town of Maunaloa, the Highway 470 drive (just a few miles) to the top of the north shore and the overlook of Kalaupapa Peninsula, and the short stretch of shops in Kaunakakai town. After you learn the general lay of the land, you can return to the places that interest you most. Directions on the island—as throughout Hawaii—are often given as mauka (toward the mountains) and makai (toward the ocean).
Most Molokai establishments cater to the needs of locals, not tourists, so you may need to prepare a bit more than if you were going to a more popular destination. Pick up a disposable cooler in Kaunakakai town, then buy supplies in local markets. Don’t forget to carry some water, and bring sunscreen and mosquito repellent to the island with you.