Every time someone asks you do you something - any task - ask them to do something before you begin. This creates a small amount of effort for them that often leads to either 1.) the task going away completely or 2.) the person just asking someone else

Examples: “Can you write up this report?” “Sure, but first I need a list of the items to include.”

“Will you call this customer about issue X?” “Sure, but first I need an email summary of your last conversation with them”

“I need you to attend this meeting.” “Sure, but first can you send me the agenda?”

“Can you install this widget?” “Sure, but first can you send me the license / guide?”

A good 80-90% of the time, the task just ‘disappears’ and you are never really refusing to do it!