The most important skill is customer service. The ability to deal with challenging clients is probably the toughest part. People are often angry at the bank, and they try to take it out on you, so you just need to empathize and offer solutions. Second, is sales. It will depend what the priorities of your management are. In short, identify every need of your client and match them with solutions, with some creative convincing if necessary. But absolutely do not pull a Wells Fargo and mislead your clients into products they do not agree to.
At its core, retail banking is a sales job. If you're outgoing, like sales and customer service, and build relationships easily you'll do fantastic.