This is a very difficult balance to strike but one that is very important if your child is to believe and respect what you are saying to them. One thing is for certain and that is that children are not stupid. They know if you are not being genuine and if you over praise they will most certainly be aware of this.
It is the quality of the praise that is important not the quantity and it should be specific to the performance or task. What is absolutely vital however in any form of praise is that the child is recognised for working hard and trying their best.
How should you go about praising your child?
Make sure that all praise is sincere, appropriate and meaningful. You should be taking every opportunity to praise the process and not the outcome, positively reinforce something done well, be clear in your praise and only say it when you really mean it.
All feedback that you give your child(although in many ways this should be left to the coach) needs to be constructive and both parties recognise that this is an opportunity to learn.
In conclusion, look to give your child plenty of process praise, they then see this as praise of their hard work and effort as opposed to praise of their outcomes. It will also help them to become intrinsically motivated and adopt the growth mindset that we have talked so much about on this site. Good luck!