"Efficient" = having a high ratio of output to input. Efficient also means means working or producing with a minimum of waste.
Examples : "An efficient test engineer wastes no time".
"An efficient engine saves gas".
"Effective" = producing, or capable of producing, an intended result; or having a striking effect. Example 1:
Example : "For rapid long-distance transportation, the jet engine is more effective than a witch's broomstick".