Here are a few tips to stay safe.
1. Stay on the trail. People have been walking these islands for centuries and if there isn't already a trail, forget about getting there. If you lose the trail, or it becomes difficult to follow, backtrack immediately.
2. On ridge and mountain trails, don't step to the side even to take a picture unless you are careful. The margins of a trail are often just ferns and grasses that disguise a free-fall.
3. Many less popular trails are unsigned. As you proceed, look back occasionally to memorize your return route. Use sticks or rocks as marker arrows (and scatter the markers upon your return).
4. Note your departure time for a hike, and make sure to begin your return when you have used up less than half the remaining daylight. Bring a flashlight.
5. When hiking in groups, stay together.
6. Always bring an equipped pack, with food, water, and extra clothing.
7. Don't let the kids stray.
8. Read No Worries Hawaii for independent traveler itinerary ideas and advice.