Look for opportunities to praise your children for genuine reasons. Be specific, tell them what they did well. Tell them you appreciate what they did. Say things like good job (and then be specific about what they did) or thank you for...
While there are times you will need to correct your children and I'll talk about how to do that in other parts of this site, you want to find genuine reasons to praise them (without overdoing it) and letting them know when they have done things well.
This will reinforce the behavior you want them to do more of.
When you need to correct your children, make sure that you spend more time, at least twice as much time, catching them doing something well and telling them about it...without any underhanded comment attached.
Sometimes, you can compliment your child ,and add that if they did it just a little differently, providing specifics on how they could do it differently and perhaps even showing them or doing it with them to make sure they understand completely, so they could improve the next time.
If you complement with added instruction, be sure that at other times, you complement them without any additional instruction (at least twice as often). You don't want your children to ever think that when they hear a complement from you they are also going to hear how it wasn't good enough or how they screwed up.
What is an Asset?
Nature abhors a vacuum