I recently took the Wonderlic test and scored high (over 98th percentile.) I did 3 things to ensure I'd get my best score:
1) Got a good night's sleep. I forced myself to go to bed early 2 nights in a row. I also avoided reading, crunching numbers or web-surfing beforehand, to keep the eyes and the noodle fresh.
2) Ate blueberries and blackberries for breakfast. Rats fed blueberries do better in a maze than rats that didn't have blueberries. For lunch, I had a small bowl of lentil soup, and nothing else, before my test in the early afternoon. An old German proverb states: "A full stomach doesn't like to think".
3) Drank lots of water beforehand. The brain works better when well hydrated. I hit the washroom just before the test, and had another big drink of water just before going in.
Also, don't take your eyes off the page, and don't let your mind wander, even for a second. You only have 12 minutes to try and finish 50 questions, so every second wasted hurts your score.