Of course you need an advance agenda for your planning commission and zoning board and thorough minutes. You know what circumstances require a public hearing. This article by the Michigan State University Extension office dives into more details.
Do your ordinance or rules of procedure specify what constitutes a conflict of interest? It might mean a member has a financial interest in the applicant’s outcome, that the applicant is a relative or that the member owns land close to that of the applicant. But how close is too close?
No member should have ex-parte contact with an applicant outside the meeting. Commissioners or board members may be allowed to drive visit the site, either alone, or all together, in compliance with the open meetings act. Again, your rules should specify what is allowed.
The article also includes a link to this page, with basics on parliamentary procedure.