The voltage that you want to Run the LEDS on would help us out
As For you resistor for each LED in Parallel It would be 68ohms 2W for each.
Most of the Time I would go with 9 LEDS. And Run of 3 LEDS in series
This would give you 3 Groups that would run in Parallel to power.
Drop your numbers into this Calc. Select Schematic and it will Draw what you need (tells you Resistor wattage and every thing) Use Solution 1! You'll need 3 X 270 ohm 1/4W Resistors and 9 2.5v 20MA LEDS. Why 9, these are not real bright LEDs so an extra will make it brighter.
If you have to use 8 (it's a pattern or so forth)
Go with the 2 groups of 4 LEDS in series with 100 ohm 1/4W resistors.
Again
Drop your numbers into this Calc. It will even give you the wiring diagram if you ask it!
By the way I assumed 12Vdc based on your numbers
Hope this Helps!
CrazyBillyBob