Learning how to do everything on the Arduino can get a little tricky when you're working with a lot of parts. Arduino forum member Romano d'Ezzelino has put together a series of handy reference cards that show the basics of a number of common connections.
Much like his pinout programs we talked about previously, these charts show off the basics of how to make a number of different connections without blowing anything up. Each card includes information such as voltage and pin diagrams. They're incredibly easy to read and a great reference guide when you're first getting started with Arduino.