Succinctness requires thoughtfulness and time.
Focus on delivering the core message, clearly.
Useless ideas should not be there.
Knowledge and skills are necessary to understand what is the core message and how to covey it.
Take the time to know the receiving end. Without such knowledge, you will never know what to say and how to say it.
Use words to the utmost of your ability. Be clear, kind, and honest.
If you can't write succinctly. Throw it away, and start all over again.
Take your time, do not rush.
Convoluted and thoughtless words do more harm than a prolonged silence.