Get the Facts First. Most clients are not lawyers. They are scattered and harried by their case. That means you have to get them to settle down and give you the facts. Then you have to check the facts because they give them to you only through their own filters. Finally you have to organize the facts.
Develop a Theory of the Case. Boil it down to one sentence that the client agrees with and can carry as a big flashing neon sign in the back of their head. This will inform their testimony at deposition and trial and help the lawyer present their story to the court. It will also help you separate the good facts, the ones that support your theory, from the bad facts, the ones that support the other side's theory.
Be Constructive. Don't make the theory of the case that the other party is the bad parent and you are the good parent. Keep the focus on the children, not the other parent. Play up your positives instead of the other parent's negatives. Instead of, "Mom never helps little Johnny with his homework" say, "I am more consistent in helping little Johnny with his homework."
Don't Fight City Hall. The Family Court System may be terrible, but we are not going to change it overnight for your case. Accept it the way it is. It is never going to be the way it should be. That means I can't get the Judge to disqualify herself, I can't get the Custody Evaluator or the Guardian Ad Litem replaced, so you are going to have to get these people on your side. If that means you have to get your own therapist or acting coach to tell you how to do it, then that is what you have to do.