If the evaluator requests that you set an appointment within the next ten days to come in, then smile and set the appointment. Never argue with the evaluator. Don't be late for your appointment. If you are supposed to pay money to the evaluator, pay it--don't try to bargain for a lower price or criticize the price. This isn't a bazaar. Dress appropriately for a professional appointment--don't look like you are ready to go to the beach.
What to do if a test is ordered and you do not think it is appropriate
If the evaluator orders you to submit to a drug and alcohol screening and you do not feel that you need such a screening, then do not argue with the evaluator. Contact your attorney and express your concerns to him/her--not the evaluator. There probably isn't anything you can do about it, because the order for the evaluation likely contains a provision that the evaluator can order whatever screens/tests that she/he deems necessary for the evaluation. When in doubt, though, take the question to the attorney. You don't want to give the evaluator the impression that you question his/her authority.
How to get your "character witnesses" into the evaulation
If you think that you are a great parent with school-related issues, then put your proverbial best foot forward by asking the evaluator to speak with your child's homeroom teacher. If you believe that you are an active and involved extra-curricular parent, then provide the names and contact information for your child's sports coach or Scout leader with the suggestion that these people have witnessed your active, appropriate involvement in this area of your child's life. Same goes with religious school teachers or youth group leaders.
Sharing messages from the other parent to show his/her bad behavior
If you have voicemails or text messages or emails from the other parent which indicate that the other parent is disparaging of you, then share those with the evaluator. Example: Voicemail where you can hear the children in the background, "You deadbeat! What kind of a father doesn't pay his child support on time?! Now, I can't buy him those basketball shoes he wants and it's YOUR fault!" Email: "You can't pick up Joey this weekend, because I'm taking him to my brother'[s birthday party in Orlando. He doesn't want to miss the party and you know how he loves Orlando. You can see him on your next scheduled time." The evaluator will not be impressed by the other parent's behavior.
Making sure your home is ready for a visit
If the evaluator comes to your home for a visit, then make certain that your residence is clean and safe. Do not have a bin full of empty beer bottles or keep your prescription medicines within reach of small children. Make certain that there are not dirty dishes piled up in a sink or dead cockroaches lying around. If you have pets, make certain that all the pet-related issues are addressed--no fleas, no dog droppings, reptiles securely caged. Basic cleanliness and orderliness counts--vacuum, dust, make beds, change burned-out light bulbs, have smoke detectors. You don't need a palace, but your child should have his/her own area with some age-appropriate toys.
Additional resources provided by the author
Ask your attorney if he/she has a guide from NBI (National Business Institute) called, "How to Help your Client Survive a Custody Evaluation."