There are three ways you can give someone a compliment:
1. The compliments criticism-compliment sandwich: your compliments have an ulterior motive, which is really to criticize someone. The person you’re giving the compliment to will realize this, and will not take your compliments seriously.
2. Complimenting something someone was born with: you tell someone that they’re smart, or they have beautiful eyes, or tall. This might brighten up their day. But it will also promote complacency.
3. Compliment a behavior: praise their good work ethic, attention to detail, their willingness to try something new in the face of adversity, or something else that requires thought and action. This is called positive reinforcement. It will encourage more of that behavior.
So if you want encourage people to get better, praise the behavior that makes them better!