How can I prepare for dental school

You don't say whether you are in school in the United States. If you are, you should have a career services office in you college. The counselors should be able to guide you.
If you do not have a career services office, most schools will have information about admissions requirements on their website.
For instance, my alma mater, NYU College of Dentistry, lists their admissions requirements here:

http://dental.nyu.edu/academicprograms/dds-program/admission-requirements.html

If you have more specific questions ask away and I'll see what I can do to answer.
Good luck!

Dental Schools are becoming very competitive in the United States, as the secret is out, it's a great career. It's important that your dental school application reflect both strong academics and exposure to dentistry, such as shadowing dentists or volunteering in dental clinics. You will also need to prepare yourself for the DAT, or the admissions test for US dental schools. There are a wide variety of books, software products, and online tutorials that help in preparing you for the test.

It can also help to reach out to the schools you are interested in attending for dental school. Ask to visit the campus, talk to current dental students, and have a meeting with the dean of admissions. This can help in the application process by letting you know what the school looks for in a strong candidate. Schools get hundreds, sometimes thousands of applicants, if you want to set your application apart from the others the dean of admissions can give you helpful hints on what they like to see in a candidate, such as volunteer or research experience.
I am often told the hardest part is getting into dental school, and I anticipate that may continue as more people see what a rewarding career field it is.