Take a moment to think about the last time you actually said “no” to anything in your personal or professional life. Whether it’s the 15th wedding that you’ve been invited to this year (and frankly can’t afford to attend) or the client dinner that your boss volunteered you for, saying “no” isn’t easy.

And it’s not necessarily just people-pleasers who have a tough time saying no. Most of us worry about what others will think if we tell them we’d rather sit-out than take part. We all want to be thought of as responsible, dedicated, and grateful for the consideration.

Knowing how to assert yourself with a polite and professional “no” is one of the most important skills you can learn, says Kathryn Minshew, co-founder of The Muse, a popular career guidance site for job opportunities and advice.

If you find yourself in any of the three workplace scenarios below, here’s how you can say “no” in the best possible way.

How to turn down a project

Your boss throws another deadline-looming project in your direction, making it difficult for you to meet your current goals. You want to impress your manager, but this isn’t the first time it’s happened and saying yes will make your next few weeks unbearable.

The next time you’re facing a similar situation, Minshew suggests pushing back with a nuanced, thoughtful response that demonstrates your consideration of business priorities. “Saying no or pushing back is never easy but try to avoid rambling in a passive aggressive way or blurting out a flat-out ‘no.’ Instead, express gratitude for the opportunity, ask your manager what his or her priorities are and then explain what’s already on your plate. After all you do want your boss to continue thinking you are the most capable person for challenging tasks,” says Minshew.

Here’s an example of how you can respond: “Thank you so much for thinking of me for this, but I was planning to spend this week working on [name of other projects].”

This gives your boss the opportunity to weigh in on what’s most important so that there can be a reshuffling of priorities and assignments in a way that benefits the entire team.

How to get out of a sticky situation

From time to time throughout your career, you’ll be faced with uncomfortable, morally compromising situations at work. Say, for instance, a coworker asks you to lie or cover up a mistake. Tactfully getting out of a sticky scenario requires a more delicate, thoughtful approach. The first thing Minshew strongly advises is not to respond too quickly, because you could find yourself agreeing to something you don’t feel comfortable with.