I've said it before, and I'll say it again. A landing page without a form is a wasted landing page. You've already spent a considerable amount of time, energy, and money getting people to visit the page, and now you have to gather their information. Otherwise, the entire process grinds to a halt.
There are only a few hard-and-fast rules about response forms, and they are:
Keep forms as short as possible. I've seen some response forms that ask for lots of information, and these invariably depress response. The more information you ask for, the less likely someone will part with that information, no matter how enticing the offer.
You may wonder what the value is from just gathering names and emails, if you really need to know a whole lot of other information, such as nature of the project, budget expectations, and buying authority of the visitor. Trust me, you can always send a follow-up email survey in a week or so that asks these people for more information, or you can follow up with a quick phone call.
The key here is to get them to fill out the form. Without that, you've got no traction.
Clearly mark required fields. Use an asterisk, color, and bolding if you have to (see my note below about accessibility). If you have 10 data fields and only 3 are required, and those are marked clearly, it'll look like a short form. People will think, oh, they only want me to fill in three pieces of information, that's OK.