Hi Raju,
Follow up is a critical element of the entire Recruitment process which is from the time we first establist contact the candidate till the time he/she actually comes on board.
At the interview stage keep in touch with the candidate to establish his interest & fit in the organization, also to find out his convinience for attending an interview. For any reason if there is going to be a delay from your end due to panel unavailability etc, communicate this to the candidate. It gives him the confidence that you are keenly intersted in his candidature.
Post interview make sure you let him know the status of the interview, positive or negative. Many times, due to other pressures we contact only the selected candidates, not the rejected ones. Care should be taken to inform rejected candidates also & if possible give them a feedback as to the reason of rejection. They will benefit from such information & will also become a messenger for the organization & won't hesitate to refer others.
Before joining, establish contact with the candidate & find out if he was able to resign smoothly or are there any issues he is facing. In case he is relocating find out if he needs help & assist him in whatever way you can. By establishing such a rappot the candidate you can make sure that he will look forward to joining your organization.
I hope this has answered your query atleast to some extent. Do let me know.
Regards,
Ranjani