How do I respond if he tries to get closer? What are subtle things guys like?

As a college student in her early twenties, I've never been close to another person. I've never been intimate in any form, and that includes the incredibly minor things like holding hands or kissing. 
There's someone I've been getting to know recently, as a friend I originally thought. He seems to slowly be showing interest beyond that. I don't know what I think about this yet, or if he's the one to pursue something with, but I've been thinking about it. 
What should I do if he gets more bold with it? It appears to me that he's getting gradually touchier (a side hug here, an excuse to touch my arm there ("nice bracelet"), etc. I'm highly observant and introverted; these things stick out, and I overthink them. 
I know myself, and I know that I could easily be caught off guard, freak out, hurt someone's feelings, and ruin a friendship. I really don't know what to do with myself if he were to try to kiss me or something. How can I be comfortable? What are subtle, non-sexual things that guys like?