Controlling an LED Strip with an Arduino

I need help controlling an LED Strip with my arduino. In the long run I need it to be vibration activated, but I don't have the vibration sensor now and would just like to know how to correctly assemble the circuit. I am pretty new to all this so I didn't have much of an idea where to start. I just modeled the RGB LED tutorial in the SIK Guide, but I feel like I am doing something wrong. I do have an outside power source, a 12 volt wall plug. If you have an idea of what to do please help, as this is for a huge project in my class.

You need a buffer between the Arduino output and generally the 3 cathodes of the RGBs of the LED strip.
A good one to use is TPIC6B595, can sink 150mA from a 12V powered strip, and commits just 3 pins of the Arduino to control as many strings as you feel like with daisychained shift registers.
If you just have the one strip, then 3 discrete transistors can be used to buffer 3 IO pins.