Advice about working in retail?

I've never had the opportunity to work in retail because i'm from a small town that, well, offers no jobs in retail. I worked at Sonic for 2 years, so I have had a job; however, I just moved to a bigger city and have had 2 interviews for retail jobs at the mall.

Journeys is supposed to be hiring me for the "back to school" rush, and I have an interview with Spencers tomorrow.

The thing with Journeys is that i'm not guaranteed my job after the school rush is over, he said we'd all have to prove ourselves with sales and overall personality. BUT, i've never worked in retail so i'm not exactly sure how hard it's going to be to "prove myself" in order to keep the job when the rush is over.

Spencers i'm not too worried about because it's not a short term job offer like Journey's is.

Any advice?