Custody of children

When a couple with children less than 18 head to courts to obtain the custody of the children what are the things that they need to know. How the courts look at this situations? Obviously it is very hard situation for both the parties as well as the child who has to see its parents walking separate. The courts are supposed to make decisions that is  almost always child centric or "Best interests" of child. The "Best interests " include the nature and kind of the home environment, stable earning,who has been the primary custodian before the litigation was brought, any signs of violence in the family on either parent by the other parent, fitness of a parent like is the parent under drug abuse or alcohol, signs of abuse on the child and many other factors as provided by family relations law. But the parents now-a-days are becoming more and more educative and less mean towards their exes that they would co-parent the child with other parent for the good of their children. The father without bitterness wither comes to exes house spends some time with the child and vice versa. The new significant others of the exes doesn't seem to have any problems with that.Of course this doesn't happen in the under developed village but the urban cities it is emerging these days so as to maintain the meaningful relation between the biological parents and the children.