Learn English – What to say if you don’t want anything from a store

I learned English as a second language. As I have never lived in any English speaking country, sometimes I don't know what to say in common daily situations.

One good example of this occurred when I stayed in US for three weeks, beginning of this year. Sometimes I went to a store, was asked what I was looking for, but I didn't know the best way to answer as I wasn't looking for anything specific, just taking a look.

What could I say in this situations, when you don't want the crew's assistance or are not looking for something in particular?

Thanks,