Hi, I used to do this in my dim and distant youth, most important thing is to pick a site where people have time and space to stand around and watch or wait their turn to be drawn. I used to target holiday makers on the beach, but I suppose a public park would do as well.
On the downside if you draw a static crowd you are also likely to draw the attention of the constabulary. Not such a problem in the good old days.
Unlike busking it can't be taken for begging, but since you are in fact selling a product you may find you are expected to pay a concessions fee for some sites.