HTML Placeholder Standards or Accepted Use

I am creating a form wizard in .net and part of the requirement is to use placeholder text in the form fields along with labels beside the form.

For example I have

@Html.LabelFor(model => model.FullName) @Html.TextBoxFor(model => model.FullName, new { @class = "form-control", placeholder = "Full Name" })

or for the hint I can use placeholder = "John Doe" or placeholder = "ex: John Doe"

Since I am using a wizard, the form has approx 50 fields over multiple tabs for data entry such that using placeholders for every field may not always clarify what is needed in which case I would redundantly put the name of the form label for consistency. Because of this I am rethinking using placeholders at all. I worry that the form will be harder to look at given the amount of fields and possible uselessness / extra clutter of placeholder text.

Is there a standard in place for what is appropriate for placeholder text given different form designs?

Is there an accepted use for when it is and isn't okay to use placeholder text?