If you don't get one, try signing in as a walk-up! That's often pretty successful.
Have you signed up for dining alerts? They let you know when a reservation has become available. You put in your date(s), party size, and preferred time (like breakfast, lunch, dinner) and it will notify you (and anyone else who has signe up for alerts) when something opens up. You have to be really fast about grabbing it.
If you want to be inside, those are the harder ones to get.