I saw the most beautiful girl yesterday, but I didn't do anything about it...?

Today two friends and I were at the store and this girl that worked there smiled at me, I smiled back, then I didn't do anything else. My friends kept telling me to go up and talk to her, but I just froze up! I didn't know what to do or what to say. So of course they questioned my manhood and told me that I'll have to talk to her next Saturday. I really want to talk to her, but I have no idea what to say. I'm thinking about going into the store and looking at the products and wait for her to come up and ask if I need help then just start a conversation from that. Do you have any better ideas? Do you have any advice on how I can prepare myself from chickening out a week from today? Any help would be greatly appreciated!