Form Default Values on Landing Page

Remember that prefill takes effect on LPS. So if a field's value is literally an empty string, that's going to appear instead of the form's default.
Can you post the URL of the LP? Also, are you testing using an incognito/private browsing window?

OK - thanks for that!

It may be that I can use an embedded form on our own site rather than the landing page. My requirements are:

1) pre-populate hidden fields with default values set in the form
2) populate one hidden custom field using a token

For #2, when the user clicks through a campaign email, this should set the token value so I don't think I need to use the landing page? Or do I? 

Still a bit of a newbie here - thanks for bearing with me.

You can still use the LP -- just turn off Prefill. I should've said Prefill takes effect if you leave it on.

OK - understood.

With an embedded form on our own site, can a custom field value be passed to a hidden field via token when a user clicks through an email campaign? Or do I have to use the landing page?

Thanks!

You can still pass values into hidden fields via cookies or query parameters with an embedded form. 

However, prefill (where an associated lead cookie automatically pulls data in from Marketo) won't work with the embedded option.