Fellow magician here!
That really depends on how much work you want to do in terms of putting together a trick, what kind of setup the stage will have, and how long you have to perform. Card tricks might not be great if you've got a large audience or aren't mic'd for explanation, and huge stage transformations might be too hard to set up, so you're best off sticking to the simpler tricks that can still be flashy.
Cup & ball tricks, scarf tricks (eg having it appear from your hand/elsewhere), the cutting string + putting it back together trick... making stuff float in mid-air can also be really fun, and pretty simple!
I'd also head to your local library-- chances are there are some "beginning magic" books out there in the How-To section, and even just flipping through those can give you a ton of ideas!