People say "fake it til you make it"; and it sounds clever. However, you're not faking it. You were hired for a reason. Someone believed in you enough to hire you over many other potential employees, so you must have something to you. You need to understand that you don't have to fake it, because the fact that you got the job means that you're not fake. Listen and learn, be a sponge. Then you'll usually understand why you were good enough to get the position in the first place, and you'll improve and be awesome!