In almost all the families I have ever downloaded, object styles are rarely if ever used. In a recent tutorial at my work I was surprised to learn only 2 people out of an office of 30 actually knew what that were used for.
For those that are confused in this area, object styles essentially tell Revit how to break down families into subcategories of its main category. In the example of a window you can categorise one solid extrusion in your families as a ‘Frame’ and the other extrusion as the ‘Glass’. When inserting the family into your project you now have far more control over its graphical representation though the visibility graphics dialogue box. You could hide the glass element of your families in some views but not others, or even change its cut pattern or line type.
So if it makes sense to do so for your office or current job, when creating your family apply the solids and lines to objects styles, especially the predefined object styles in categories such as windows and door families.
Dimensions to Reference Planes
This is a big one! If you can, place a priority on dimensioning to reference planes and not the modelled geometry. Once you have dimensioned to the reference plane, then lock your geometry to that reference plane.
To be perfectly honest, if you are doing a simple box then there might not be a lot of need for this, and there is such a thing as too many reference planes (one of my other pet hates). But it is an important habit to get into, a well thought out family finds a balance the amount of reference planes and clear common sense constraints.
Nested families are so incredibly useful, and sometimes necessary for effective family operation. This could be a whole tutorial in its self, but for now, just know that nested families are invaluable! But again, find a balance.
Another area often overlooked is the in-family visibility settings of each object, this is important to consider if you want your family to be versatile at different detail levels. This, like object styles, can be something that is more personal to the way you might use the model in your office environment or during your project stages.
Formulas and Equations
This is the one that always scares people the most and the one where people opinions on the best approach varies greatly. But the repeating theme throughout this whole summary applies here also, keep it simple. The more complicated the equation, with branching variables and formulas dependent on other formulas, the slower the family will operate. I am guilty of this over and over, and it takes practice to realise when you are beginning to over complicate the formulas, but don’t shy away from them. Even if you aren’t a math wizard, simple formulas are still powerful.
All the standard math, trigonometry, and IF/OR/AND statements/equations are open for you to use with the parameter constraints you have applied to your family.
Formulas are essential in adding intelligence and user-friendly operation to your families. An example one of the primary formulas I use to prevent users over or under stretching my families is a maximum and minimum formula.
Length A = (User entered value)
LengthMaxMin = IF(Length A > 2000, 2000, IF(Length A < 10, 10, Length A))
In this example the dimension of you object is applied to the ‘LengthMaxMin’ parameter. The user enters the desired value into the ‘Length A’ parameter box. LengthMaxMin then checks that it is not above or below the values of 2000 and 10 respectively, and if all is good, adjusts its dimension to match ‘Length A'.
If you are having trouble understanding the equation I find reading it as a sentence in this manner helps:
If Length A is more than 2000, then 2000, otherwise if length A is less than 10, then 10, otherwise Length A.
Not that hard when you phrase it like that.
Now there are many other little tricks you will pick up along the way, but these are some of the big ones that you need to consider. Good luck creating your own families and I hope this has helped. Feel free to get in contact if you need help or guidance with your own family creation.