Pug is a sensitive breed,breeding them is not easy.
i am breeding pug from past 4yrs & believe me its not easy to breed them.
still if you are interested in breeding them then you should start meeting pug breeders check their female pugs and their puppies, stud males.Meet every pug breeder available nearby your locality.You should research for a month then start with a pug puppy avoid buying adults and semi adults.
(beagle is also a nice option)
Dog Behaviour Specialist