The interview process I went through 4-5 years ago is different to how it is now, but being a hiring manager, I can provide some great insight:
Focus on the online application first! You want to have a passion for fashion, be honest, and be someone who truly enjoys customer service. You must pass this first stage since it is an evaluation that will let us know if we should call you, or not! Do not bring in your resume, or do a meet and greet before this!!!
After you have completed this, it never hurts to make yourself known, ask for the hiring manager or GM and introduce yourself. Be personable, dress GAP, and show genuine interest! This way they can look for your name and make it a point to want to interview you. Depending on the season, size of the store, and general need for new associates, it can be a group or 1on1 interview.
The Key: Every manager will have their own interview style, be aware of this. ALWAYS Be friendly, personable, SMILE, and show your passion for fashion. LISTEN to the questions and provide clear examples, not general. Always contribute an answer if asked! Sell yourself, be realistic and let them know how your experience can help them meet their sales and Gap Credit card goals!
Good Luck!