it is best if you use an attorney if you don't know what you are doing. I realize they are expensive, but well worth it to get things done right. Once the initial custody is determined it is difficult to change.
theFAQ to the left are a good starting point for newbies. Also Cheyenne wyoming has a step by step guide for filing pro se. Even if you are not in their state it is a good reference tool. You might also want to check the website for your areas court. The may have pro se clinics and workshops.