The most pesky issue in both my personal and business life is saying "no", and I know others who find it just as challenging.
Seth Godin has a great post on his blog "On saying 'no'". It is 60 seconds that will lead to lower stress and higher productivity. My favorite is "If it's going to distract you from the work that truly matters, pass."
Read Seth's entire post here... http://sethgodin.typepad.com/seths_blog/2016/03/on-saying-no.html