Customer Retention Strategy: private member health clubs

"Identify the critical factors that form a successful customer retention strategy."

I'm writing a literature review of the above question and don't know which topics need to be included.

I've looked at relationship marketing but need to include service quality, customer satisfaction, customer expectations and customer perceptions.

I need a detailed and structured essay plan, covering all the aforementioned points and any more you would consider important.

The case study is on private member health clubs.