The best analyst briefing decks that I've either seen or helped build are not filled with marketing messaging. They clearly layout what analysts typically care about, which could include the following: trends you've observed in market you operate in, the challenges your product(s) solves, overview of your growth trajectory, industries you touch plus key use cases for each, unique differentiators, and insight into the product & (high level) GTM strategy and company vision.
Other elements I'd suggest: Include customer success stories, lay out the ecosystem that supports your products (ie. partners, integrations, develop engagement), and share how you support your customers. Also, it may seem obvious, but I'd caution against including stats/proof points that were produced by another analyst firm. In general, have a clear agenda that includes space for Q&A and listening to their feedback.
Getting better at messaging can entail a few things and can depend on what exactly you want to improve (ie. having strong frameworks/structure, consistency in writing styles and tone, persuasion, etc.). However, what I always strive to get better at is storytelling. A few books that either directly or indirectly offer what I've found to be great gudience for how to tell engaging and meaningful stories include:
Blink, Made to Stick, Start with Why (I'd suggest watch the TED Talk), Obviously Awesome (disclaimer: I haven't read this book yet, but have heard great things about it). I'd suggest exploring behaviral or social psychology books as well.
What makes the best product pitch (deck, one pagers, videos, webpages, etc.) is that it is not a standalone asset. I've see lots of strong product pitch assets, however, if they exist in a vacuum/individually rather than as part of a larger journey or campaign then they can become forgettable pretty quickly.
The assets that usually stand out to me are the ones that clearly articulate the problem being solved and have captivating CTAs that lead the audience to the next relevant part(s) of the learning journey. Your user may not always follow the desired path, but giving them the opportunity to hear/see/read about what challenges your product addresses, how it works (and fits in with other products), why it's best solution for them (now) across different mediums helps to build momentum with your message. Also, with decks, (demo) videos, and one pagers--the more concise, the better.
Running focus groups (with a diverse collection of existing customers and another with prospects) has been one of the most useful methods that I've leveraged to test messaging. Presenting a few different narratives and messaging options directly to your target audiences, and listening to them share what resonates and doesn't resonate (and why) can provide concrete insight in what message(s) would compel them to take serious interest in your offering.
This largely depends on the size and distribution of your sales team. On one end, if you have a small, locally based sales team then this is managable and usually lower effort than what you'd need to do on the other end of the specturm for a massive sales team that is highly geographically distributed, and that is also aligned to customers in different segments and/or industries. In general, ruthless consistency and over-communication via multiple formats (one pagers, slide decks, websites, FAQs, enablement videos) goes a long way, as does getting them to actively participate (ie. through messaging certifications, having their peers coach and test them on the messaging, etc) in fun ways--you'd be surprised what infusing a fun theme or some costumes can do. It can also help to align the messaging to different stages of their selling methodlogy.