Finding a job is actually a full-time job in and of itself. So every once and awhile you need to cut yourself some slack, stop hitting refresh on the job board web page and step outside. See from friends. Call your mom. Your whole life can’t be work, and it won’t be even if you get the job (well, hopefully it won’t be). Plus the desperation and frustration will come through in an interview. I’m not saying don’t take every opportunity seriously but cut yourself some slack. You’re not the first person to be without a job for awhile and chances are this won’t be the last time you’re between opportunities (by choice or not). You have other things going on in your life that are important too!
People will say thank you cards are unnecessary after an interview and some recruiters even say that thank you cards sway them one way or the other. But I would argue that even if you don’t get the job HR people will always remember those who send them a thank you card and maintain contact with them. Thank them for their time, remind them about something you chatted about, and show that you appreciate their consideration. Write it immediately after the interview and either drop in a mailbox or give to the receptionist to hand in for you. Nothing too flowery or long, and make sure you sign your last name as well.