First of all make sure you research the company you are going to be going to. Have they got a website etc. and at some point in the conversation throw in 'yes I saw on the website that blah blah, or I saw in the literature etc.' that shows you have been doing your homework. I know nothing about the industry but presumably you would have some pics with you to show them. Try to mention an interest outside of the field which will show you are an interesting person i.e. I collect old Box Brownies or something, or I am interesting in photographing planets (or hope to in the future) Above all be likeable, and smile a lot.