Practice makes perfect
Practicing does not only make sure that you develop your skills, it also creates a more confident and polished performance. And that is what you want to show to your boss, colleagues or clients! The more you prepare yourself the better you perform. Eventually it will become more natural and you will feel more and more confident.
It is not only important for an athlete to fuel and rest your body, it is also important for you as a professional. It keeps your mind clear and keeps you energized. Take enough breaks where you can. Go for a walk or for a quick bite. Taking a short break like that can definitely release some tension. If you don't have the possibility to leave your workspace, then try to close your eyes, take deep breaths and clear your mind for ten minutes or so.
Keep on worrying about that stressful task or about that important presentation, doesn't help you. It will only delay you which will end in even more pressure. Make sure you get these tasks out of your way by immediately tackling them. It will definitely lower your stress level and it will make your overall goal manageable.
Do not doubt or question yourself. You know you and you know your skills. So don't have and definitely never show a lack of confidence. Ofcourse you can be insecure about some things but make sure you won't focus on that. Instead focus on your skills and on your accomplishments. Stay positive! The more positive you are the more you will believe in yourself and what you are worth.
What you don't want to show is any feelings of fear or intimidation towards your boss, colleagues or clients. Everyone can become temperamental when they are stressed but the magic trick is to stay calm. Try to not to contribute to a tensed atmosphere. When you're feeling rushed, pause for a moment, allow yourself to step back mentally and take some deep breaths. Also, even though it is not easy at all, take criticism with a grain of salt. Do not focus on negativeness, think before you react and don't let anyone's poor attitude make you feel bad.