Effective (adj.): Adequate to accomplish a purpose; producing the intended or expected result.
Effectiveness is mostly about an ability to adequately accomplish an intended purpose. It constantly measures if the actual output meets the desired output. It focuses on the outputs
Efficient (adj.) Performing or functioning in the best possible manner with the least waste of time and effort.
Efficiency is a ratio of quality representing an ability to maximize the outputs with minimal inputs. Although we can focus on the output side of efficiency most often we focus on the inputs.
Being effective is about doing the right things.
Being efficient is about doing the things in the right manner.
If we accomplish the purpose, we are effective.
If we maximize the outputs with minimal inputs, we are efficient.