Whether you're an employee or a contract worker, one of the hardest things you'll ever learn is how to say no. You don't want to communicate that you're ungrateful or that your work ethic is lacking, and you want to keep trust and communication going--but in some situations where your time and energy are already overcommitted, or where you know that

Here are some common situations in which you might need to turn down work, and what you can say to maintain your credibility:

1. You need to enforce boundaries. If you're the kind of person who is always saying yes, you need to be more vigilant about creating and maintaining boundaries for yourself. You're allowed to say no without feeling lazy or worthless.

Say: "I wish I could help, but I know I couldn't give it the time it deserves right now."

2. You're already stretched too thin. A never-ending to-do list and perpetual exhaustion are not great workplace assets, and you need some real evenings and weekends with down time to be effective on the job.

Say: "I'd love to help out with that, but I already have . . . and I don't want to shortchange that commitment."

3. The project is outside your expertise. It's good to stretch your skills sometimes, but accepting a project that lies far outside what you comfortable doing can lead to frustration and a loss of self-confidence.

Say: "This project looks like a fun challenge, but--unless I'm misunderstanding your instructions--it definitely falls outside my skill set."

4. You need to stall. Maybe there's a project you really would like to do, but you're too overloaded at the moment to even think straight. Or maybe you know you should turn it down, but you don't yet have the will to say an outright "no."

Ask: "Can you please send more details so I can fully review this before making a commitment?"

5. Scheduling is an issue. When you are swamped, it's okay to step back and assess if you have the time to take on something new.

Say: "I know this is an important project, but I don't think my current workload will give me room to meet the timeline."

6. You want to stop being an enabler. If you have people-pleasing or enabling tendencies--the kind where you often step in and do other people's jobs, even at the expense of your own work--you probably already know that's a habit you need to give up.

Say: "I know it can be overwhelming at first--I can't really take this on right now, but let me give you some tips to help you get started."

7. You want to keep the option of future work open. Your plate's not just full but completely overloaded--and that's when someone you've always wanted to work with comes to you with a project that you would love to take on. If there's no way to rearrange things without compromising your standards.

Say: "I appreciate you thinking of me and I would love a chance to work with you on this. I'm already completely booked up this month, but I really hope you'll ask again next time."

8. The project seems pointless or redundant. If it looks like pointless busy work, it probably is pointless busy work, and your time and energy are too valuable to waste.

Say: "We're working to stay tightly focused on our mission and goals, and I'm afraid this project falls outside the parameters."

Always be tactful, polite and professional, and keep the focus not on yourself ("I'm already working nights and weekends") but on the work ("This project deserves more time than I can give it right now"). If you know someone else who might be a good fit for the project, offering to connect them is a way to keep things positive.

Frightening as it seems, it really is possible to turn away work without hurting your reputation. In fact, it may benefit when you're seen as someone who's in demand and who has the confidence to say no.