I've found that the key to longer rides is to make a plan, and stick to it. Know how much you need to drink, how much to eat, when to stop, and so forth. And be sure to stick to the plan. It's easy when you're feeling good to just keep going and not take a break, or to not eat a bar or a gel. But skipping what you know you need will get you on a longer ride, because you can't get it back. And it really stinks to get close to your goal and not be able to finish.