Self esteem has had a fair amount of focus in recent decades and yet the understanding about what it is and how to get it still needs a bit of fine tuning. You see self-esteem or self-worth is not about being cocky and confident as I have heard a few people declare, I think it is about total and utter self acceptance - warts and all.
Unfortunately, we live in a competitive society with a relatively narrow idea of what 'success' constitutes. Much focus is given to these limited success criteria, starting at school. So one way of developing self-esteem in children is to praise the non-academic features you notice they excel in such as humour, kindness, being thoughtful etc
But I think a more important way of helping your child to develop self-acceptance (which leads to self-worth) is to help them understand that nobody can be naturally talented at everything. It is good to accept the areas we struggle with compared to others and appreciate it is just part of what makes us, us. It is absolutely fine to not be brilliant at everything. It doesn't mean you cannot learn to get good in things you are not naturally talented in, it just means you will have to put more effort in than someone who finds it easy (which, you could argue, is even more praiseworthy - motivation and determination could well be more impressive than natural talent!).
And children are not daft, they soon know within their class who is good at maths, who is not so good at reading, who is brilliant at running fast etc. You can't keep this awareness from them. So best just 'give permission' to be less than great at something.
This is one of the messages I dedicate a whole page to in my latest book, What's going on inside my head' by Molly Potter, out later this month.