Familiars are animals, maybe people I don't know, that have a close connection to you, I have two at home! You can have multiple familiars all the time, they are just animals you are bonded with. If you can make sense of that great!
Finding a familiar is pretty similar to finding a partner, (like gf or bf). Say you're a woman, over time you meet many men, then one day you find the one that is the right for you. You set out with an intention of finding someone but (hopefully), you don't force a relationship with the first one you meet.
With human partnerships, it helps if you have good social skills, and are comfortable with yourself. That way you attract the right person for you. So, with animals, start off by learning how to relate with them. Find out what they do and don't like. Above all, be yourself.
I have always kept cats, it feels natural to me. However, with the many cats I've had over my years, just one of them was the right one for me. She was my close friend and teacher. You can't force it. You will know when your familiar comes along, because they will tell you :)