1. If you want to build something, spend a lot of time on it. This goes hand in hand with "practice makes perfect", the more you do it, the better you become at it. Being open to everything around a Wiki and trying everything out, requires time and effort.
CSS basically. I try out a lot of stuff, modify elements that are already present on the Wiki to fit the theme more, just general snazzy stuff to add more and more cool things to your own Wiki. If it's just one trick, then I'd say I like to add border-radius to everything, from thumbs to the WikiaRail, infoboxes and other templates.
Ask me about
They should probably ask "Hey, I'm having problems with this one thing, can you come and take a look at my Wiki?" Chance is I'll come and clean up the whole place for you!