Many jobs are difficult to learn due to their complexity. Rather than annual reviews, I strongly recommend that any leader implement monthly reviews. It sounds overwhelming at first, but such frequency offers many benefits, and having people do well at their jobs saves more time than monthly reviews take.
Monthly reviews help ensure your employee is exhibiting the skills expected for the job, is completing the tasks expected of the job, and is supporting customer service by showing your clients the best of your company. What is the damage done to your company if a client doesn’t think you’re responsive? If they think you’re difficult to work with? What is the effect of not having people complete their tasks, and you not realizing it right away? Going several months without verifying a person’s work and documenting their accountability is a management mistake that can create vast leadership problems.