Follow-up after interview...

Is there a better way of making a follow-up after an interview? and how often shall I do this or shall I do the follow-up at all? I have sent a 'thank you' card the day after I had an interview. Thank you.
I wouldn't feel bad about calling the interviewer once to follow up and express your continued interest in the position. After that, if you don't want to feel like a "nag," you could call Human Resources (if applicable) and see if the position has been filled or what the status is on the interviewing/hiring process. Best of luck to you!

A card is nice but, consider sending an email thanking them while also highlighing some of the positives you bring to the table. When I receive these I take note when the person makes mention of one or two of the things I talked about with them. Also, near the end of an interview, ask them for a tour of the unit/area. The more time you spend with them the better your chances. When I am being interviewed I close with "Is there anything I need to do (or skill) to be a stronger employee for you". This tells them I want the job, I am willing to work on weekness if they see one, and it makes them view me in the position. I had one boss tell me that is what sealed the deal for him.

For the future, I always make sure I ask at the end of an interview, "When do you expect to make a decision?" It's a fair question and usually the response will be "Within two weeks" or "at the end of the month." Then I send the thank you card to each person I spoke with. If I haven't heard anything by the time the interviewer specified, I call then.