There have been times in my career where I've felt like a complete impostor. I'm sure I'm not alone in this. I still get this feeling when I start a new job. I start thinking, "I hope they don't find out that I'm unsure of this decision," or "Was I wrong to ask that question? Did it make me look like I have no idea what I'm talking about?... Because I don't!" It leaves this cloud of worry and panic of being found out that you don't know as much as you thought you did when you started the job.
In some ways, these kinds of experiences are good. It keeps me humble. The further I went into my career the better I've felt about my skill set. Still, there are two main factors that helped me change from feeling like an impostor to feeling knowledgeable and empowered: experiences and confidence.
Experiences
Over time you gain a better understanding of how the world works. You will have a variety of experiences (some good and some bad) that teach you about the working world, business processes, and working with different people.
These experiences take time to acquire. Patience is the key. Hopefully, as you go on in your career you are learning from your mistakes and earmarking your triumphs to use again in similar situations.
Not every situation you encounter will be the same. By using the experiences in your repertoire you will have an easier time navigating your newest hurdle.
Confidence
Now when I say confidence is the second key to not feeling like an impostor I don't mean that you project an exterior confidence, but still shrink into self-doubt on the inside. Instead I mean that you are confident in what you know and unafraid to say when you don't know.
There is no shame in being confident enough to ask, "What do you mean?' or "Explain that to me," or even to say, "I'm not sure I understand." Early on in my career, I was afraid to challenge others, especially my superiors' decisions. I didn't want to seem dumb in a room full of people that seemed to get it. Over time, this fear dissipated. Now, asking questions often gets everyone in the room thinking differently about the problem at hand or even the solution.
Conclusion
Feeling like an impostor is something many people face in their jobs and in their life. What you don't want is to have it get in the way of what you can achieve. Feeling unworthy of praise or downplaying your accomplishments isn't something that you should have to struggle with on a daily basis. While it is sometimes good to be humbled by new experiences, you should be proud of the talents you do bring to your job.