What are the biggest career mistakes to avoid? originally appeared on Quora - the place to gain and share knowledge, empowering people to learn from others and better understand the world.

Answer by Mira Zaslove, start-up and Fortune 500 manager, on Quora:

I've made my fair share of career mistakes, and also managed a lot of early career employees. The biggest mistakes I've seen often come when people are working too hard, but not working on the things that matter. People who succeed are able to master that subtle art of being assertive, productive and also politically savvy.

Not knowing what you want and/or not advocating for what you want

  • If you don't know what you want, you aren't going to get it. It's key to know what you want both in the short and long term. Good opportunities are missed when you aren't prepared to seize them. People who move forward in their careers often know what they want at every step. Career advancement is also often give and take, so it's also important to be flexible and adaptable - with the bigger picture in mind.
  • Managers cannot read your mind, and the squeaky wheel often gets the grease. This is a mistake I've made more than once. Doing a good job isn't always enough. Promotions and high profile projects often go to those who ask for them, not always those who are best qualified. If you don't ask for it, you likely won't get it.
  • One of the biggest career mistakes is to not advocate what you want and to not have a plan of how to get it. Be clear with management about what you want. For example, years ago I managed a charismatic and likable guy. People wanted to help him and he often had people asking him what he wanted. However, he rarely collected on this goodwill because he didn't know what he wanted and wasn't able to give people a clear action. Be ready to clearly explain what you want and why you should get it.

Working too much

  • Grinding all day, every day, is a recipe for burn out. Being over-worked rarely leads to your best work. The people that work the hardest, are not necessarily the ones who advance. Working smarter is better for your career in the long run. Slow down and prioritize. Be open to new opportunities. It sounds strange, but working too much can limit your long-term career prospects.
  • Of course, if you are working on something critical it is important to give 100%. However, it is unlikely that all of your work is mission critical. All of the time. So, work on the things that matter. Keep your strength to be able to shine, when it counts the most.
  • Prioritize the projects that will lead to the highest degree of visibility and return. Keeping your head down all day won't give you the exposure you need to know when, and what to prioritize.
  • Delegate when you can. True leadership comes by letting other people shine. Remember: the people who get credit for the work, are not necessarily the ones who do all the work.

Forgetting that other people are key to success

  • It's a big mistake to think that you can do it all yourself. You can't. It's important to nurture and maintain good relationships. Make eye contact and smile in the hallway. Chance encounters at lunch, the hallway, or in a meeting can make all the difference.
  • It's also a big mistake to try to prove to others how great you are. Rather, it's better to compliment others on the work they do. Let them know if you are working on something complimentary. Talk about how your work relates to theirs, and how you can help them. Ask questions and listen. And along with point #2: Listening is surprisingly hard to do when you are exhausted and overworked.
  • Successful people inspire confidence. They appear in control and relaxed. Especially when they aren't. People respect calm. They will trust important projects with people they believe can handle it. A big mistake to avoid is to lose your calm and say something you will regret. Once you've said something, you can't take it back. Be careful with your words. Changing somebody's mind is difficult and exhausting. And it rarely works. Spend energy building on where you already have agreement.

This question originally appeared on Quora - the place to gain and share knowledge, empowering people to learn from others and better understand the world. You can follow Quora on Twitter, Facebook, and Google+. More questions: