Permission to fail: It is normal for your child to experience setbacks and challenges, do not try to shelter them from these valuable expereiences, allow them to overcome these obstacles.
Mindset language: Use the language of a growth mindset such as 'effort' 'perseverance'. 'growth' and 'you can'
Describe the behaviour, not the person: Do not label them - E.g. instead of saying 'your lazy' tell the young person that they are not putting in enough effort. Phrasing criticism in this way allows the person to see that they are capable of doing things differently. (In other words, give criticism from a growth, rather than a fixed, mindset)
Ask for a specific change: Think through in advance what you want your partner or child to change. There is little point in criticising someone's work or behaviour without having a clear idea of what you want them to do differently