I realized a while ago at work that when you ask someone to do something you have to include a few key elements if you actually want it to get done. This is particularly relevant in a work environment.

1. Give it a due date. Most people prioritize by due dates and if the due date is "whenever" then your thing will never get done.
2. Give the motivation for the task. "Do X" is not nearly as useful as "I want to achieve Y. Please help by doing X."
3. Give the information necessary for the job. Is there documentation on how X should be done? Is there a set of articles related to X that people should know? Send those along with the request.
4. Ensure the person actually has the time/clearance. At work this means "get permission from their manager" but in the every day world this means "make sure they aren't already overloaded."

If you skip some or all of these there's a huge chance that the task will not be done or will not be done well.

"Managing up"

On the flip side, if someone says to you "Do X" without doing these 4 steps it's totally reasonable to say "Sure, when do you need it? What's our overall goal? Do you have any documentation on this? And I'll need to talk to my manager to get permission but should be able to do it."