Effective is an adjective used to describe success in producing a desired result.

Sentences:

1. The medicine was really effective in curing his problem.

2. The actor gave an effective performance in the movie.

Efficient is an adjective used to describe a productive human or a machine.

Sentences:

1. The machines used at the assembly line were highly efficient.

2. She is an efficient worker, and should be rewarded for the same.