Read through the Lemegeton, and you'll see that many of the 72 have the same attribute: "Gives good familiars." But what does this mean?
A familiar, as many know, can be an animal or spirit that serves the sorcerer. What does it take to make a familiar? Not much. Any pet or passing imp can potentially be a familiar. So why do you want a 'good Familiar'? Because not all familiars are truly capable.
A good familiar casts for the sorcerer in the subtle realms, carries energies to their targets, protects the sorcerer, guides the sorcerer, collects information for the sorcerer, and more. And these goetia familiars? They are typically skilled in most, if not all, of these areas. That's why so many spirits are known for this in that work.
Now, this isn't a universal definition. For instance, in Obeah, a familiar is another term for the 'head Bones', so to speak. One of the Bones family, whether it's one we know or one revealed through direct revelation, chooses the sorcerer, and bonds with them to act is their main Bones. But, the same functions apply.
So how does one get one of these familiars? Simple. Do the evocation and make your request. Make a pact. Ask an experienced worker to help you. Or find and contract a passing being. If you have a pet that can take the spirit into themselves, even better. But whatever you do, I suggest you get into contact with a good familiar.