However, it is safe to introduce your puppy to other dogs who are UP TO DATE with vaccinations, but make sure they are friendly and healthy first! As long as they don't touch the ground or have contact with unvaccinated dogs you can also start taking them out and about - eg in the car or by carrying them. The "critical socialisation period" is thought to be from 3-12 weeks old (although some sources quote up to 16 weeks of age) and as many puppies will not have completed their vaccination course by 12 weeks it is vital to start thinking about different and safe ways to socialise them.
When you first introduce your puppy to a new stimulus, eg a vacuum cleaner, start slowly. For example when you first turn it on have the puppy in a different room, or when they first see the vacuum have it switched off but push it around.