Hygiene is a set of standard precautions to prevent the spread of contagious disease. These precautions generally try to either kill contagious material or to remove surfaces that hold contagious diseases.
Hand washing - this is perhaps the most basic hygiene precaution, and one of the most effective. Most diseases can live on the skin for long periods of time, and the hands are the part of people that are most frequently in contact with other people. Surgeons go through a very thorough procedure to wash their hands before surgery, but even a simple hand wash is very effective for even intimate contact with a patient. Soap and water works better than alcohol based disinfectants.
Gloves - Gloves protect both the patient and the doctor from organisms that can penetrate or irritate the skin. However, although hospital gloves are sterile, they do not replace hand washing and the two should be used together.
Smooth surfaces - Most hospital surfaces are deliberately smooth and tile grout and fabric are avoided whenever possible. Smooth surfaces are less likely to harbor germs and are easier to clean.
Clothing - Cuddy's wish that House would wear a lab coat is not without foundation. Normal clothing can hold stains that hold germs. Lab coats clearly show stains, are easy to discard, are cleaned frequently (daily, or more often) and are thick so that blood and other fluids cannot easily penetrate them. Kutner's aversion to ties is also a good idea - unless they are worn with a clip, ties can easily become contaminated and, because they are infrequently cleaned, hold germs for weeks or longer.