Focus it and pare it down to its simplest, clearest, easiest-to-understand form.
Avoid the temptation to add features or extras or that last minute thing no one thought about until the very end. The more you stack into a message, the more discombobulated it will be. The more it will push pepole away instead of drawing them in.
Make its expression fun or funny or interesting or informative or delightful. Anything but boring. Make it so compelling people have to read it.
This doesn’t just apply to communications. We can apply this to all forms of writing or art or commerce.