You have to live as if you have free will. You can't say, "I've considered all the possibilites, and have decided that there is no free will", because considerations and decisions are acts of free will themselves. Of course, that doesn't mean you have free will.
I find it interesting how people often cite determinism as incompatible with free will. Our minds don't violate the laws of physics, but they still make decisions. Similarly, a car can still be described as "driving", even if the physics behind it are deterministic.
