If you are spending time with a boy who you are interested in, it is vitally important that you let him know you want to be more than friends. Otherwise, he won't know, and he may be too polite to make a move on you. While you could just tell him you like him, the odds are that you aren't going to want to do this, because it's taking a big emotional risk. Rather, you should tell him subtly by breaking the touch barrier. This will indicate that you're into him in a less-aggressive manner, thus leaving you less open to rejection.
Brush him as you walk past him, or brace yourself on his arm or shoulder to lean into something. This is a good way to break the touch barrier because it will leave him wondering if you did it on purpose or not. It will also look incidental, so if he doesn't like it he can just assume it was an accident.
Touch him on his arm when you agree with him or if you're laughing at one of his jokes. This will make him associate you touching him with you generally feeling positive around him.
Stroke his hand if he's telling you something that generates sympathy. It doesn't have to be something terrible, but even the slightest sad story can earn a hand stroke. It's OK to act more sympathetic than you actually are if you want to break the touch barrier.
Touch him a little more every time you touch him, as long as he responds well. So if you first patted his shoulder, you can next touch his upper arm, then stroke his forearm. Increase the amount you touch him slowly, though, so you don't come on too strong.