The huge amount of preparation and research that me and my family put into the assessment was a key in obtaining the custody outcome I got. Beyond all that though, it was all true.
You can prepare and research all you want. That increases your chances of success. But nothing beats being a good parent who truly puts his/her kids interests at the fore!!
Funny - Our lawyer left her firm just as we got the acceptance from the OCL. Our new lawyer was a useless piece of... well... she didn't tell us anything about the investigation, how to prepare, or even when it was... We went into it completely blind. We were very lucky (and naive) in many ways, but our approach of trying to do the best by the kids worked wonders.
We didn't make a big deal of it with the kids. We told them that a lawyer that works for children was coming over to talk to them because occassionally they do that with families to check and make sure everything is OK. At the same time they admitted to the OCL that apparantly mom had a little chat with them just before the 1st OCL visit where she was slamming her hands together yelling (because she was excited) that they HAD TO tell the lawyer the right answers to his questions and who they liked more. When one of the kids came to me and asked me why she was so upset (and saying that she was making them really nervous), I told them that mom is just nervous because she was meeting a new person (she's quite shy and our child bought my excuse for her). I went on to tell her that the lawyer will be asking them a few questions. If they don't know the answers they can say that. If they are unsure but think maybe they know the answers they can say that. If they are absolutely sure of the answers they can say that and if they change their mind about any of the answers they can tell that to the lawyer too. I told them that there were no right and no wrong answers. Either way it wasn't a big deal and to think of it like a nosy family friend is over!
With the actual OCL investigator we never actually said that mom has no bedtimes, etc. We just stated that we had X bedtime and that we felt it was very important to be consistant with our bedtimes, as the kids were often tired when we pick them up. Subtle hint... He then asked the kids what their bedtime was at mom's... answer: none aren't we lucky we get to stay up until midnight whenever we want .... dad's.... answer: 8:30 every school night and 9:00 on weekends which sucks eh (says the youngest). In hindsight I realize that if we had gone at the investigator up in arms screaming that the kids stay up until midnight every night that they are with mom because she is a useless parent, they probably would have thought that we were
1. exaggerating (how would we know when the kids go to bed every night unless we were interfering and questioning them about the other parent's custody time - being controlling)
2. suddenly making up a bedtime to look like better parents (trying to one up her)
3. complaining about what she does and not trying to help the kids
4. proving mom right - we can't communicate and we are judging and slagging her - no chance for 50-50
Instead we came across as wanting the kids to have a meaningful relationship with BOTH parents and if we have to take up the slack for the lack of rules/discipline/sleep/nutrition and be called the bad guys by the kids then we were OK with that, but we made it very clear that they absolutely needed us for the structure and learning part of their upbringing.
The ruling was that it was "absolutely essential" to the children that no time be taken away from dad. It was "absolutely essential" to the children that dad keep his 50% custody time and say in how the children are raised.
Moral of the long story; If you can figure out the weaknesses of the OP, try to accept that not everyone is good at everything, and try to make up for them in your child's life then you will be doing a great service to the child. And a happy bonus - you will look indespensable to anyone outside of your family trying to decide upon custody time. You will surely benefit from doing your research, as DTTE did, but I think that the #1 rule is keep the kids best interests at the front - and usually those best interests include a meaningful relationship with BOTH parents. Even if you are the one fighting for more time make sure that you can praise somthing that the other parent does (truthfully).
Good luck at the CC