For DD6, we're accomplishing by finding things that don't come naturally to anyone, and then we talk to her about the value of practice, let her know mistakes are natural, and encourage her to put in effort, and reward her for the same. Once she sees her practice paying off with improved skill, it becomes its own reward.
In her case, it's been an ongoing process, beginning about since she was 3 or so. Examples include bicycling, gymnastics, and guitar. She's also playing soccer, and the coach awards one or two "player of the game" to the kids who exhibited the most effort, regardless of whether they scored or not.
She still has a tendency to beat herself up and become excessively frustrated when she doesn't get things right the first time (hello, perfectionism!), but there's been a gradual improvement in her sticktuitiveness. I remember her first weeks in soccer, she managed to convince herself falsely that everyone else was much faster than her, but she never considered quitting.
Hope this helps.
