Develop your soft skills as much as your audio skills. You can be the best sound designer in the world, but if you can’t write a coherent email, show up on time or behave in a humble and professional manner, you will have a hard time building your career.
If someone asks for revisions, do them. We have to remember it's their "baby". We may think we nailed a music cue or sound effect. But for whatever reason the client may not. It's their call :) Above all, stay passionate and excited about what you do! We truly are fortunate to make music and sounds for a living. Or, if it's not your living yet, you're still very fortunate to have your gifts and talents.
The great artists are the ones that can convey a lot with very little. Learning how to edit one’s self is one of the key core concepts of great game audio design—and, frankly, design in general. Too often, unskilled artists try to put too much into their audio design. But I can tell you from experience that working within self-imposed limits forces artists to be more creative and more decisive.
You can never give up and you have to believe in yourself when no one else will. You can have all of the talent and chops in the world, but you have to be prepared to eat macaroni & cheese 3 times a day, live in a roach infested apt and accept rejection with dignity.