How will be however you find best. There are. A variety of materials and guides. Many people like chads videos and just study them, alongside the dat destroyer, and bio review book of their choosing. Others take Kaplan/dr Romanos course in New York. It really is to your discretion.
When? Depends on if you want a gap year after college where you can travel, enjoy your last year of freedom, or if you want to go into dental school right after college. Applications start going out in June, and you preferably wanna get your application in with the first batch, your chances are better. The admissions cycle takes about a whole year, so my application is going out this June, so that I can hopefully begin dental school in September 2014.
DAT studying takes about 2 months to get a good score. And you want to take it after you've taken bio 1,2 chem 1,2 and orgo 1,2.