In proposal writing, your first step should always be to gather information about the party who will judge your proposal. That's because you want to present a proposal tailored to that party's specific needs and knowledge level. In other words, you need to put yourself in the other party's shoes and look at the situation from that party's point of view. If you are pitching to your boss or your company executives, you might already understand their positions and their concerns. But if you are pitching to people at another company, then you will need to do a bit of work researching who they are, what they do, and what their needs are. Yes, that research can take a bit of effort, but putting in that effort makes your proposal much more likely to succeed.
Generally, a newsletter is meant to do two tasks: informing people about something or persuading them to do something. For example, a newsletter may inform your clients about your new product or inform them to check out the company's website for the latest information.