How you present yourself to an audience, and in fact, how you gather that audience will have a huge impact on your success. Large, colorful props are the best way to draw attention. The more space you can fill, the more heads will turn. Balloons are an ideal attraction. With little effort, you can have large numbers of people looking your way. Unfortunately, a lot of balloon twisters find themselves immediately surrounded. People will steadily push themselves forward to get as close as possible. The logic being that the closer they are to you, the better their odds of getting a souvenir.
When gathering a crowd, make sure there's a line between yourself and the audience. Any line, real or imagined, is fine, so long as you get to position the crowd at the distance away from you that you want. There's nothing wrong with asking people to back up, or even physically nudging them back in a gentle and polite fashion. Some buskers place a rope on the ground in a circle about their working area, instructing their crowds to stay behind it. I sometimes chose some short children and place them in the front row, informing everyone that they are the front row and that they need to stay where they are in order to see. I'll also point out that when looking for volunteers, I never choose anyone that walks onto my "stage". At the threat of not receiving a balloon, it's incredible how quickly people will step away.
Some performers work best with large crowds in the hundreds. Others work best with only a few people around. The size of the crowd you wish to perform for is up to you. If you want to build an audience of several hundred, it will take time to get them all together. You need to start entertaining and building curiosity from the moment you step out on your pitch. While the formal show has started, the entertainment needs to go on as long as there is any audience at all, or they'll walk away. Once you've spent all that time doing the build your show has to be powerful enough to entertain everyone and make them want to pay.
Other performers prefer to do shorter shows with smaller crowd builds. You can gather a crowd of 50 people much faster than you can build a crowd of 200 and you can fit more shows into the same period of time. I happen to like the smaller crowds of 30-50 at a time since it makes it possible for me to get a little more personal with the crowd. I start up faster, I get the show going more quickly, and I get a larger percentage of my crowd to toss money in my hat when there are fewer around.