Until your puppy has completed his course of vaccinations (around 12-14 weeks) he should only be allowed to mix with other fully vaccinated animals. If you have other pets, introduce them gradually to the puppy and never leave them alone together at first. It is very important for a puppy to meet a variety of other animals and people as soon as possible. Once his vaccination course is finished try to get out and about with your puppy - there are also puppy 'socialisation classes' where your pup can meet others of the same age for fun and frolics. Think about attending puppy training classes - bad habits learned early are hard to break!