Simple rules for dummies; I have violated most of them. (It’s good to have some sense of adventure.)
Carry food and plenty of water. Know where food and water are available on your route. Have flexible layers of clothing. Use sunscreen. Carry a map. Your cell phone won’t work way out in the boonies. Don’t take an unsafe or poorly maintained bike out on an adventure. Carry appropriate tools and supplies including a tube, patch kit, and pump. Know how to fix a flat tire. Don’t be afraid to spoil the aesthetic perfection of your bike by putting a bag on it. Tell people where you are going and when you expect to be back. Know your level of conditioning and your limits, and choose your routes appropriately. Look at the elevation profile for your route.