Praise the Effort, Not the Child
Saying what your child did is more useful than saying how clever they are.
"You kept trying until the tower stood up" tells a child something they can do again. "You are so clever" does not, and it quietly raises the stakes for the next thing they attempt.
Notice the specific thing: the careful colouring, the patience with a younger cousin, the second attempt after the first one collapsed.
When something goes wrong, describe it plainly and move on. Children take their cue from how we handle a spill or a mistake.
Avoid comparisons — with a sibling, with a cousin, with the child in the next flat. A comparison never makes a child try harder; it only makes them watch the other child.