What important skills are required for a customer service position?
LISTEN to the customer, use your manners, and don't be one of those awful cashiers that ignores people while she finishes a conversation (a social conversation like what your plans are this weekend) on the phone or with a co-worker. The customer is the reason you are getting a pay check, at least act like you appreciate it. Be genuine as well.
And if you will be using a cash drawer and don't have experience with one, when a customer hands you a bill or bills, lay them across the till drawer until you are finished counting their change back to them. You could lose a lot of money due to cheaters and liars who will insist you gave them change for a 10 but they actually gave you a 20. Oldest scheme in the book. Laying it out before you put it under the clip is undeniable proof of what you were handed.