Effective Vs. Efficient... The definition

Effective (adj.): Adequate to accomplish a purpose; producing the intended or expected result.

Efficient (adj.) Performing or functioning in the best possible manner with the least waste of time and effort.

Efficiency refers to how well you do something, whereas Effectiveness refers to how useful it is.
Effective means that something works. Efficient means that something works well.
Effective is doing the right things. Efficient is doing the things right.
In summary, 

If you don’t do the right things, but do them very well, you still are not moving toward the result you want. If you do the right things, but execute them poorly, you will end up expending more energy and thought than necessary, leaving less energy for other tasks.

The great thing is, with one of us being effective and the other being efficient, we make an excellent team.