I have taken DAT twice. I didn't study much, but PAT on my first trial and scored AA18 TS18 PAT23.
Then I retook and scored AA22 TS22 PAT 26.
This is what I did:
I spent about three weeks reviewing science (Chem and OChem) by using CHAD'S VIDEO. He is the man especially if you forgot basic concepts. If you understand and know how to answer his practice quizzes, you will at least get 19+ on ochem and gen chem. For Bio, I read the AP BIOLOGY twice and made notes about things I forgot. (I majored in Bio, so felt pretty confident) Once I was done with reviewing, I started doing DAT Destoryer problems (twice). Once I felt pretty confident with every subject, I took TOP SCORE practice exams and took the real DAT.
It took me about a month and half to prepare for the DAT.
Good luck.