The older generation would probably nag and told you and your baby to stay confine to the house for at least the first month but times have changed, and most babies have to leave the house for doctor/medical appointments. I know most mummies usually use this chance to take a quick stroll at the mall to have lunch because it's too boring to always be at home. Like Hui Qun mentioned, if you wish to bring your newborn out, avoid crowded places and make sure that there's always a clean baby room for you to go to in case you need to change diapers or feed him. I never realized how important this is until I became a mummy myself!
There is really no specific guideline on when you can bring your newborn out. Most propose that once your baby is out of the hospital, it is fine to bring him/her out if you feel up to it. The only thing to note would be to avoid large, crowded, enclosed places with poor ventilation. For such places, it will be good to wait till your baby is six to eight weeks, when her immune system is better developed. These places increase her exposure to airborne germs that could be dangerous for her immature immune system. Bringing her out for walks in the parks will be great. The fresh air and sunlight would do you and your baby good! :)