Don't: Let others bash either. Make sure your relatives and others who speak to the evaluator follow the same rules about not bashing the other parent that you do (see: Tip #5: Don't Bash).
The evaluator is probably going to to ask you for a list of "collateral contacts." These are third parties who are supposed to help the evaluator get a full picture of how the child(ren) is doing at home, at school, and at any extracurricular activities. Your collateral contacts should not all be your family members because these are people who are going to be appear to be predisposed to say only the best things about you and bad things about the other parent. In fact, it's probably better to focus on neutral third parties such as teachers, counselors, coaches, ministers, daycare providers, and other people who aren't automatically in your corner. However, family members are sometimes interviewed as well. If the child regularly spends time with the grandparents or you have a new significant other who is part of the child's life, then the evaluator is going to want to talk to them.
Your friends and family members are going to want to paint the best picture possible about you and may want to say all the bad things that they know about the other parent. They will want to help and protect you and this desire to help can backfire and actually do you harm. Remember the caution from Tip #5 about how if you have nothing to say about the other parent but bad things, that it will seem like you are not willing to facilitate a relationship between the child(ren) and the other parent, or worse, that you are trying to actively alienate the child(ren) from the other parent? Well, the same thing can happen if it's your collateral contacts who are doing the bashing.
Do: Make sure that your collateral contacts understand that the cautions from Tip #5: Don't Bash apply to them as well and explain that they should be looking at everything from the perspective of what is good or bad for the child(ren) while also understanding that it is important for the child(ren) to have positive, meaningful, long-term relationships with BOTH parents.