Good luck to you Isi-B!
I'll throw my two cents in here (I know I know... the collective groan heard around the world) There are a couple of standby things that I always look for when I interview people-
1) Shoes - should be clean and polished
2) Fingernails - not chewed
3) Watch - wear one... the right way on the left wrist
1&2 tell me you not only care, buy are aware that your appearance reflects on you and who you work for.
3 tells me that you're aware of time. If you don't wear a watch, and I'm not saying it has to be expensive, just a watch. If you don't have a watch, how do you know what time it is? I know, I know... we all carry 20 mobile devices which tell us the time, but a watch serves no other purpose so it tells me you're cognicent of time management.
lastly, a firm diliberate handshake with good eye contact is key. keep us posted. Good luck my friend!