There are different grades of clean room and, depending on your needs, it gets more and more complicated.
The simplest kind of clean room has operators in a cotton lab coat and before you enter you change your shoes then put on a hair net and gloves. The air is changed on a regular basis and this air is filtered before entry. As you walk in you pass over a sticky mat on the floor. That's it.
Next step up. Proper clean room gear including hat, goggles, face mask, trouser coverings and covers over your shoes. The air is put through electrostatic as well as ordinary filters and you walk through an airlock that a) blows all the dust off you and b) maintains positive pressure inside.
Full clean rooms have all of the above but the air is changed much more often and everyone who works there is paranoid about dust and contamination. The layout of the room is designed according to the desired airflow, walls, floors and ceilings are specially coated, the temperature and humidity are tightly controlled and nobody wears makeup or perfume. If you come back from a sunny vacation then expect to be banned for a few days until you stop shedding skin particles. Forget about working there if you have a cough or a cold.
Note that a clean room is not just about dust, it's ALL contamination. This includes eliminating oils and greases from the area and monitoring your supplies to make sure that you don't introduce something that will increase the particle count. Open the wrong box of lab tissues and the paper dust could shut down your entire production process, scratch your nose with a gloved hand then handle a wafer and you could contaminate a million dollar piece of machinery.
Now try and fit all of this into a box