Practice

It's not enough to just be smart... you also have to be quick! 

Here are some brain training sites that can help with buzzer speed and memory.

There's also a quiz bowl style question and answer practice website that uses pyramid style question-asking (from general to specific). The faster you get the answer, the better! (WARNING: Unregulated website with other online players... can be like the Wild West... ask an adult before you use this site)