Firstly a Saint Bernard is a beautiful dog and a great choice.
The best thing you can do is go to one or two lessons at puppy school. I have two dogs at the moment. A bull Mastiff and a chocolate brown Labrador.
The bull mastiff we took to puppy school and he was so shy he would hide under the chairs and squeak. Now because we did those lessons loves other dogs and is not shy at all. he also listens and obeys commands.
The Labrador didn't go and what a wasted dog. They are so smart but she just doesn't listen They are used as hunting dogs and guide dogs but ours just doesn't listen. She needed puppy school so it shows you what a difference two lessons make.