What do I need to prepare for my tax reduction appeal hearing?

I filed a property tax reduction appeal by last year's November 30th deadline (in Los Angeles, California / Los Angeles County). So I just received a letter from them stating that I have a hearing scheduled for this coming April. So I have 2 questions.

1. What do I need to do to prepare for my tax reduction appeal hearing? I found out that I just missed a public orientation meeting last month, (given by the assessment office) that helps people to prepare for this hearing, yet I am not sure if they will have another meeting between now and my April hearing date.

2. What is the best way to get "true" comps in order to provide for this hearing? I have heard about hiring a company to do this for me, yet I was wondering if there was a way I could easily get these comps for free by doing my own research. Yet maybe I might need a professional. However I only used the comps that I found in Zillow, when I filed for "Decline In Value Request for Review) back in June last year. However the Assessor declined to reduce my taxes at that time, thus is why I requested the assessment appeals board hearing.