I think that it's important to perform a variety of tricks and routines in a set, show or act. The variety will provide your show with different props and effects. But more important than props or effects is the difference in the audience's experiences, which can include participation and interaction, comedy, story-telling and more. The goal is to vary the approaches in your tricks so audience members can react to different aspects.
As an example (and using tricks here at Magic.About.com), if you are performing a series of close-up card tricks for friends, you can create variety by mixing up the tricks. You can find a spectator’s chosen card by causing it to rise out of the deck; mysteriously deal yourself a royal flush; allow a spectator to cut to four aces and end with some playing cards somehow adhering to your hand, as if by some unseen force.
In this set, instead of performing four tricks where spectators select a card and then you find them, you've created a set with four different experiences and interactions. To really mix things up, you can add tricks to your set that make use of coins and other props.
Speaking from personal experience, my stand-up show has evolved a lot over the years and most of the tricks that I first performed are no longer in my show. Many of the tricks that I brought in were specifically chosen to bring in new audience experiences.
One final thought about improving your sets and adding variety, in my article on 7 Themes To Improve Your Magic, I discussed seven themes that can add new angles to common magic tricks, many of those that are taught here on Magic.About.com.
So when you're looking to add a new trick, take a look at what you are already doing. And if you want to improve your show or set, take a look at what you already perform and figure out what's missing or what can add a new audience experience. Your show will benefit from the analysis.
