I like to keep things brief. Only use as much time as you need. Don’t over explain or repeat things unnecessarily.
I try to use this in my game design. I want the game to play as quickly as possible without feeling that the experience was rushed or cut short.
I try to use it in my rules writing. Because of this, I often avoid stating things that happen as a result of following the rules I did write. This can cause confusion though.
When you are writing rules you are trying to explain a system that is very obvious to you, because you invented it, to a person that likely has none of the assumptions that you take for granted. You may even disagree on the definition of the words you are using. This makes it necessary to state what you think is obvious, because it almost always isn’t obvious to the reader.
This leads me to another trick I’ve started to use when writing my rules. If I find myself using a lot of words to describe a mechanism, I cut it from the game or drastically simplify it. If I don’t have the patience to write it out, I can’t expect a player to have the patience to learn it.
Be clear, but be brief.