Your Pug will need a nice sudsy bath every 2 or 3 weeks. It is vitally important to never use human shampoo or other human baths products. Dogs can get very irritated skin rashes from these products.
You should place your Pug in the bath after you have filled it with 3 inches or so of water. There's no need to fill the tub any more than this, since having the body fully emerged will not allow for a good scrubbing.
Running the water while a dog in the tub can cause him to become skittish, so it is recommended to have the bath ready ahead of time.
Having a non-slip mat will help your dog keep his footing on an otherwise slippery surface, avoiding an accidental dunking or injury.
Check the temperature using the inside of your wrist, to make sure that it is not too hot which can irritate the skin.
Wash the head and face very thoroughly and carefully. Using a soft washcloth, clean inside all folds of the skin.
Work your way down the body making sure to scrub all areas including the genitals, legs, tail and under belly. Use a conditioner as well, since shampoo alone can be drying, which leads to breakage.Conditioner also adds a layer of protection from the drying effects of the sun & wind and friction damage.