After the interview is done you should definitely send them a nice handwritten card through the mail or hand delivered.
2. Stay in touch!
The best follow up to an interview is a consistent, sustained follow up. Why? Because things change over time. Just because someone didn’t have a lead for you six months ago doesn’t mean he won’t have one for you today. But if you’re not top of mind with him when that opportunity comes up he may not even remember you. So, remember that the informational interview is just the beginning of your relationship. Here’s proof. I once met with an informational interviewer who was introduced to me by a former work colleague. Over my career he referred me into two positions and he even placed my friend’s sister into a great job. One guy resulted in three jobs. And to be honest, I was really terrible at staying in touch with him. I was lucky that I had a great relationship with that former work colleague of mine who worked with this guy. But if I went back in time I would have managed the relationship with this guy much differently and stayed in touch more frequently.
3. Develop a CRM
You need to build your own Customer Relationship Management (CRM) system. What's a CRM? It's a database of all the people you have met with along with their contact information, notes on what you discussed and any other relevant information about those people. CRMs are great because after a few weeks you begin to forget stuff about people ("What was his wife's name, again?"). This makes is really easy to get in touch with these folks and keep your conversation relevant.
4. Schedule your follow ups
It's easy to commit to putting information into a CRM, but it isn't necessarily easy to make time for following up with those people, especially six months, 12 months, even a few years after you met with them. Schedule a day in your calendar once a month to follow up with people you've met with. Make the time, or else you'll never do it. In fact it's the easiest thing to drop, so dedicate yourself to this.
Everyone you meet with is a potential link to your next great job. But people don't think of you if you're not on top of their mind. This is where even the best job seekers can drop the ball. They assume that because the original informational interview is over (and it resulted in no leads or a job) that they’ll never need to talk to that person ever again. That's a big mistake. When you consistently follow up with folks who have taken the time to meet with you, not only will you be top of mind when a job opportunity comes up, they'll also naturally think of you because you have distinguished yourself from all the other potential candidates they have met with in the past.
And that’s the best follow up ever.