I have make some survey to learned about it. This what I have understand and I wanted to share it here :
First, you should ensure that you have a suitable baby bathtub for the job. Preferable, use a bathtub that has a sloped base, and line the base with a non-slip mat. Fill the tub with lukewarm water, testing the temperature with the corner of your elbow.
The first thing you need to do is to wash your baby's hair, behind the ears and neck. You can do this before placing baby into the water, and you can keep his cloths on until after you've washed his head. Don't wash his face - that will probably only make him struggle! You can use sterilized cotton dipped in cool sterilized water to wipe his face before or after his bath.
To bath baby, place him gently in the bathtub whilst supporting his head, making sure that he doesn't hit his head if he should kick or push himself upwards! Use a soft sponge to scrub him gently. Splash the water all over his body for a good wash, avoiding his face and ears. Most importantly, don't miss any crevices.
You should ensure that you support his neck with your forearm. With the same hand, grip around his armpit securely. This will ensure that baby doesn't slip from your grip and injure himself. Use your free hand to lather and scrub your baby.
Once you're done bathing baby, lift him out of the tub making sure you maintain your grip around shoulder and with your other hand support his bottom. Transfer him onto a towel, wrap it around him and dry him off. Apply some nappy cream, put on his cutest baby outfit and you're good to go!