Depending upon your attitude towards magick and your familiar, you might want to consider how you can protect it magickally during rituals and at other times. If your familiar wears a collar, protective sigils or symbols can be drawn in ink or scratched into the collar with a sharp instrument or protective amulets and talismans may can be hung from the collar.
Of course, this is all very well in the case of cats, dogs, or even rats, lizards, or ferrets, which can wear collars. However, if your familiar is a bird, fish, spider, or snake, a collar is out of the question. A bird could have a small amulet clipped on to it's leg, but if your familiar is a snake or fish, protective amulets probably aren't an option, but if they are going to remain within a container of some sort during the working, protective items may be put on it.
Another method for the protectction of a familiar is petitioning a deity which is protective of the species of familiar you have. Bast can be petitioned to protect cats, Lamia to protect serpents. Research may be necessary, but most animals have a deity which can be called upon to protect them. A consideration when calling upon a deity to protect an animal is that it does not confilict with whatever other entities you wish to work with.
If you use circles or anything similar, it should be noted that your familar will not necessarily stay put. You really don't want your cat to idly wander through and break a circle when you've got something on the other side howling for your blood.