Before you submit a resume to an employer, make sure it does the job. Ask somebody else to read it and give you feedback. Edit and re-write until it does. Preparation is paramount. Blow your own horn, but be careful not to go overboard with the self-praise.
Balance is key.
Now that you're prepared to talk, get ready to listen. Don't focus so closely on selling yourself that you don't listen carefully to what the interviewer says and asks. Demonstrate that you're a good listener. Learn as much as possible about the company before you go to the interview. Find out as much as you can about the person who will interview you, through networking contacts or industry trade journals.