A family is the most integral part of Revit. It plays a major role to complete a modelling of a building. Whereas, when it comes to model a family in Revit, many heads get down with ignorance.
In brief, it can be said that to model a family in Revit, reference planes and reference lines find a crucial role in it.
Also, defining of proper and adequate parameters is something to be considered critically. Further, family types, family categories, and parameters should be assigned with proper care and as per the requirement. As it is the information that builds the model which is the core concept of BIM.
Assigning right material properties is also an important factor.
Make sure to model any family from a scratch. Try to avoid linkage of other families as much as possible, so as to keep the size of family minimal and have a better performance with the system.
Keyboard short-keys get handy a number of times while performing such tasks. It may be noted that not every family can be made parametric. There are some families which can be fully parametric, while some have a limit for this functionality. The more the geometry of a family becomes complex, the less are the possibilities to add more parametric properties.