I work as a cashier at the moment. I don't like it, but I need to do it, so I go to work and 'put on' an attitude that I will enjoy it while I have to do it, otherwise I wouldn't be able to keep on doing it. I also sort of approach it (and most other social situations) like an actor might approach a role. I consciously observe other people's behaviour and speech, and add them to my 'acting' repertoire. After a while the acting becomes easier.
I also made a point of writing down the exact processes to follow for ALL transactions/dealings on the registers, just in case, at least until I'd memorised them. Usually I only tend to have stuff-ups when a customer needs me to do something that isn't part of my repertoire of processes. Luckily, though, I have some nice co-workers to call on when I need help.
The only other problem I have with it is that it's mind-numbingly boring and hard on my feet.
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Hope is the thing with feathers, that perches in the soul, and sings the tune without words, and never stops at all. -emily dickinson