Below are a few things you can start to do now to preserve your right to parent your children:
File first. It gives you an immediate advantage, as it’s the first word with the judge and can set the tone of the case.
If possible, enter ex parte (unilateral) order that reflects your current custody situation. Although the order can be modified later, the ex parte order gives you the first say in the custody battle.
Document what the current custodial situation. Gather any proof you may have of what you do on a daily basis as the children’s primary caregiver and proof of the children’s relationship with you.
Have witnesses ready. Have witnesses that will testify about your relationship with your children. Not say “he’s a great dad", but people who have seen you and your children interact and can explain how that interaction took place and your children’s reliance on you as a parent.
Don’t deny your spouse time with the children. Judges frown upon one parent keeping children from the other parent. Even if you’re the primary caregiver, it is important that your children maintain a relationship with their other parent.
Be prepared to negotiate. Most child custody decisions are a result of negotiations between the parents and their attorneys.
Don’t bad mouth your spouse especially in front of your children. This hurts your children more than your spouse, and judges will not tolerate this type of behavior.