We all like being near and working with people who say 'Yes' and who make stuff happen. It's contagious.
But there is also power in 'No'. And this is one which far fewer of us wield correctly. Sure there are lots of naysayers who will explain in graphic detail why something can't be done. I'm not talking about them. They cast a negative vibe which none of us needs in our lives. I mean the power of an affirmative 'No', if that's not an oxymoron. Saying 'No' to the minor, trivial stuff which distracts us from our greater goals and mission is an essential, and often under-used skill.
Saying 'Yes' to everything indiscriminately doesn't help you and is unfair to your team. You only have so much time and energy. Both are finite. It's up to you where you allocate those resources. Saying 'Yes' to the non-essentials is easy at the time. It feels good to commit, to help people and to see the smile on their face. But only if you are able to deliver, otherwise you are eroding that trust and letting your team, and yourself down. You'll get snowed under a weight of peripheral actions which prevent you making the big stuff happen.
You have to say 'No' to the minor things so you can say 'Yes' to what matters. In fact, individuals and organizations are often defined as much by what they decide not to do as by what they say 'Yes' to.
So next time someone asks you to do something, think about your goals. What's important? What can you and you alone deliver? How does this request fit within that framework? And if it doesn't, then simply say 'No' to it. If you explain why, you'll probably be amazed at how understanding people can be. If it's important, the task will get done. If you're not confident in saying 'No', then practice in declining a few minor tasks. Perhaps it's just proof-reading an email for someone else, or assisting with the admin. You're not being mean or unhelpful - you're saying 'No' to this so you can say 'Yes' to something more important. And over time, that will help you say 'Yes' to the things which really matter.