Unfortunately, not every employer provides a thorough list of expectations or questions for you about their project.
While vague project descriptions can be a bit confusing, you should capitalize on these opportunities by demonstrating your knowledge and experience right off the bat. Show your client that you can identify their problems and propose solutions proactively and you've already taken a big step toward closing the deal.
For example, a common question that I was frequently asked when applying for new projects, was if I had done this exact type of job in the past. Now, I anticipate and answer this question before they even have the chance to ask me directly. In my initial reach out email, I'll include a link or two over to examples of successful campaigns I've ran in the past (demonstrating my ability to replicate these results).