Focus on the achievement, not the individual
You should praise the achievement or piece of work, rather than praising the pupil as an individual. By praising the pupil as an individual, they may doubt themselves when they are not experiencing success. For example, by telling a pupil they are clever after succeeding at a task, they may assume they are not clever when they are not experiencing success. This affects their confidence and resilience.
By praising the piece of work, you enable the pupil to reflect on what went well objectively. Focus your praise on how the pupil achieved success, so they can replicate the approach in future.
You should refer to the fact the pupil has tried hard and/or consistently over time. This shows the pupil that by putting in effort in future, they can achieve success again.
Make sure your praise is specific about what exactly the pupil did well. You could link praise to targets relating to learning, or to school values for good behaviour, to make the praise specific. You can then support pupils to understand what targets to aim for next.
You should link the praise to your rewards system as set out in your behaviour policy, so that pupils get recognition for their achievements.
Demonstrate the behaviour you'd like to see
Staff around school should demonstrate the behaviour they'd like to see from pupils. For example, if staff hold doors open for pupils carrying heavy books, then pupils can emulate this behaviour.
The headteacher could also model this level of courtesy towards pupils, so that pupils can see your position in school doesn't affect how you behave towards others.
When you praise pupils for adopting this behaviour, you reinforce pupils learning by copying an example of good behaviour, rather than having to be explicitly told.
Members of The Key for School Leaders have full access to a range of resources on managing pupil behaviour, as well as a wealth of other subjects on www.thekeysupport.com/SL.