Remember, the most effective LeadForms are interactive (i.e. they don't feel like filling out a form) and help visitors their ideal outcome (something that helps them get closer to the outcome that led them to your website in the first place).
Example: What questions should an agency ask?
#1: Keep it simple
In order to deliver this custom proposal, the agency would likely need to know four things: The URL of your current website, a brief description of what you want, your budget, and a method of contacting you (email or phone) to send the proposal to once it's complete.
#2: What's the ideal outcome?
Let's say you're interested in hiring a web development agency to build your new website. You probably would want to know:
How would they propose the project is carried out?
What would be the cost and timeframe of the project?
What case studies/examples do they have of building websites similar to what I want?
So, the ideal outcome for a visitor would likely be a free custom proposal that outlines these three things. Therefore, the LeadForm (or the landing page the LeadForm is embedded on) should make it clear that this is what visitors will receive in return for completing it.
#3: Segment & personalise
Let's say the agency knows that WordPress web development projects are particularly profitable for their company. They may want to add a question in their LeadForm that asks 'What platform do you want your website to be built on?' with options like WordPress, Drupal, Magento etc. This serves two purposes: It enables the agency to segment its leads into 'buckets' and identify which leads are higher quality, and it also enables the agency to personalise their proposal and interaction with the lead, based on their answers in the LeadForm.
Tip: You can see an example of a web development agency LeadForm, by going to the Choose Templates page and clicking the 'App & Web Development' template.