If you’re going to ask someone to take on a responsibility, make it short. Not the responsibility… but the “ask”.
If you make the “ask” long and wordy, it will communicate that this task you’re offering them is so huge, so massive, so immense, that you have to take a long time to ask them. Instead, make it short.
“Hey Bill, could you lead a growth group night in a few weeks?”
Don’t say anything else. Just stop there. Let them answer. If they say no, that’s fine, all the words in the world probably wouldn’t have changed their mind anyway.
If they say, “Maybe” you can ask them what their concerns are, and you can address those concerns.
If they say yes, you can then go through the details they need to know.
If you make the ask BIG, then you’ll only freak them out by the apparent BIGNESS of the task.
MINISTRY PRINCIPLES & PRAGMATICS 
I love this! I often fall into the trap of thinking they have to know what they are letting themselves in for before I’ve even got a sense of how willing a servant they are….short, clear, get the response and then the details.
I agree, but think it can often be helpful to give people an idea of the commitment involved in saying yes. For example, rather than asking ‘can you be on the forge rego team’ I would be more likely to say ‘can you be on the forge rego team; commitment involves a half hour meeting in the week before forge, arriving to the campsite an hour early, and helping people register as they arrive’…