How do I not look like a bot

When making HTTP requests (mostly POST, as that's where things start to make a difference), which headers should I set (and what other things I have to do) so that a website won't think I'm a bot? User-Agent is an obvious one, but aside from that? I know that websites sometimes use JS to recognize legitimate visitors, and maybe the way cookies are handled?

No guys, that a serious question. Can't we just talk a little?