Praise their effort, not their intelligence.
I am smart, the kids’ reasoning goes; I don’t need to put out effort. Expending effort becomes stigmatized—it’s public proof that you can’t cut it on your natural gifts.
Dweck had suspected that praise could backfire, but even she was surprised by the magnitude of the effect. “Emphasizing effort gives a child a variable that they can control,” she explains. “They come to see themselves as in control of their success. Emphasizing natural intelligence takes it out of the child’s control, and it provides no good recipe for responding to a failure.
…Dweck’s research on overpraised kids strongly suggests that image maintenance becomes their primary concern—they are more competitive and more interested in tearing others down. A raft of very alarming studies illustrate this.
If you want to learn more, read Dweck's book Mindset: The New Psychology of Success. Want to read a controversial book about how to instill hard work in your children? Read Amy Chua's Battle Hymn of the Tiger Mother.