Time at work is finite. Every yes to a request commits to a no on something else — usually your own priorities. Women say yes too often by default at work, then struggle to deliver on commitments because the work doesn't fit the available hours.
Where to practice no first
Meetings that don't need you (decline politely, ask for notes). Volunteer roles outside your actual job. Tasks that should go to others but default to you because you'll do them. Last-minute requests on Fridays. Optional networking events that drain rather than serve.
What good professional 'no' looks like
'I can't take that on this week. Can it wait until next Monday, or should it go to someone with more bandwidth?' Brief, professional, offers alternative. Not apologetic.
Practice in low-stakes situations first. Builds the muscle for the higher-stakes nos that protect your real work.