Hygiene is a common sense issue. Remember that you will be in close contact with other people, so please take steps to ensure that everyone has an enjoyable experience.
Some good ideas for good hygiene:
Wash your gi (uniform) after every practice.
Shower or bathe before practice.
Make sure your hands and feet are clean before practice.
Use deodorant, toothpaste and mouthwash as needed.
Keep your fingernails and toenails trimmed and filed.
Blood
Blood is an area of special concern with regard to hygiene.
If you find that you or anyone else is bleeding, even a very small amount, please cease practicing immediately and inform the instructor, so that he or she can get it cleaned up and get appropriate medical attention.