Having a good gas-tank is the staple of the elite MMA fighter.  If you want to make it to the top, then you'll need to work on your strength and conditioning.  Increasing your cardio and anaerobic capacity requires training techniques that might be viewed as unconventional in other sports.  This is due to the high-intensity nature of mixed martial arts, where you're exerting 80-90% in every single movement.

Because of this, it's important to to gather all of the resources and information possible.  If you're interested in becoming a MMA of UFC fighter, but aren't really sure where to start, then this is a great place to get beginner information.  I strongly suggest you check out Eric Wong's Ultimate MMA Strength and Conditioning below, as it's a great resource.  Either way, I hope you enjoy your stay and learn something new about MMA.