Choose the right type of ribs. Baby back ribs are often a good choice as they tend to be more tender than other types.
The first essential step is removing the membrane (also known as the silver skin) that's on the bone side of your ribs. This is tough and does not render down during cooking.
Seasoning: Before you cook the ribs, season them with your chosen spices or marinades. Allow them to marinate for a few hours, or preferably overnight in the fridge.
Slow cooking: The secret to tender, fall-off-the-bone ribs is slow cooking. This can be achieved by baking, slow-grilling, or using a slow cooker. For baking in an oven, wrap the ribs in aluminum foil and bake at 275°F (135°C) for 2.5-3 hours, depending on the size of your rack.
Optional step - After slow cooking, slather your ribs with your chosen barbecue sauce and grill for additional 10-15 minutes, or broil them in your oven. This will give you a nice caramelised finish.

Remember, while "fall off the bone" is a commonly used term, ideally you want your ribs to be tender yet still have a bit of chew, as completely falling apart could mean they are overcooked. However, it all comes down to personal preference in the end. Enjoy your cooking!