Copywriting has all sorts of rules and tricks to make marketing messages more effective.
Here's one of the tricks:
No matter if you're writing a web page, a brochure, an ad, or a prospecting letter, write to just one person.
Another one of the "rules" is to know your audience, so start there. Think of one person who is in your target audience. Visualize them. Then write as if you were talking to that one person.
Pretend that it's a personal letter - just as if you were writing to a friend. If it helps you focus, go ahead and write their name - you can edit later.
Some copywriters (the ones who get paid $15,000 to write those magalogs you get in the postal mail) spend a lot of time creating a profile of the typical person in their target audience.
They use their market research, then specificy everything including age, family, job, income, health, political leanings, and much more. Then if they don't personally know anyone who fits the profile, they choose a magazine picture, give it a name to go with the profile, and put it by their keyboard as they write.
Of course it seems silly.
You aren't fooling anyone. They know that your letter is going out to dozens, hundreds, or even thousands of people. But as long as your voice is talking just to them, it will still feel personal. And personal is important if you want to connect with them and show them that it's in their best interests to like and trust you.
Writing to just one person will give you an added benefit - it will prevent you from breaking another one of those rules - saying "all of you" or "you guys."