Saying 'yes' gets a bad rap. It's the popular thing for entrepreneurs to counsel people to learn to say 'no.' But the thing is, saying 'yes' leads to way more opportunities than saying 'no' ever will.
Saying 'no' doesn't get you out of your comfort zone, saying 'yes' will.
Saying 'no' is valuable when it comes to personal principles and specific commitments, but for everything else, saying 'yes' will only open doors and push you to exceed your own limitations.
If you have a lot on your plate, that's a good problem to have. So say 'yes' to your clients, your boss, your spouse, your kids, your friends. Say 'yes' to things that will push you in the direction you want to go.
'No' is a powerful word. Save it for those rare occasions when you need to stand by your values. But saying 'no' should never be your default answer. Try saying 'yes' to everything. See where it elevates you.