Constructive interview feedback enables unsuccessful candidates to understand why they were not successful and may give them ideas for improving their interview techniques. Feedback may seem like a chore but it is helpful to the candidate and leaves a positive impression of your business.
A useful approach is the 'sandwich' structure where you start and end with the positives - even if it is just their punctuality or their enthusiasm - and put the feedback that might be hard to hear in the middle.
Then move onto areas for further development. For example, you could suggest that they develop their skills in database management as this is an important area for your business. This may encourage the candidate to reflect on how they presented their skills and to provide better examples in the future.
End on a positive note. If you were impressed with them or a particular aspect of their interview, tell them. Thank them for their interest in working with you and wish them good luck in the future. Avoid saying you will bear them in mind for future opportunities unless this is genuinely the case.