Yes hooking up series can work. IF you know about what forward voltage the leds need, add them, then find out what resistor you need to make input voltage down to what they need.
I prefer parallel hookups unless you're going absolutely crazy with lights like Smiley, or the Christmas commercial Coca-Cola trucks. It's a few more solder connections, but i think it simplifies things
+ .. Resistor ... + led 1 ... + led 2 ... and so on
- ....................... - led 1 .... - led 2 ... and so on
Actual pic of the layout, scroll down to the car bumper picture.
http://www.rctruckandconstruction.co...ad.php?t=12930