An excellent good luck charm would be something that represents something happy to you, something you love. Sunshine for example, represented by a sun or a disc is a positive happy energy form for some people. Some people make a good luck charm out of the picture of one of their kids, because that's what they love and what makes them happy when they look at it. Some people choose a Jesus medallion or a Saint they love for a good luck charm. Some love crystals so for those, a nice crystal makes a good luck charm.
Have a think on what you love, and what makes you happy. Something that brings out the best in you, something that you can give a kiss for luck and you can instantly feel something, a shift, like something has changed.
You can experiment with different things too, and over time learn to match different charms to different occasions or topics.
Most importantly, remember the HAPPY = LUCKY connection. Things that make you happy are those things that attract luck.