Hi or some other variation of that seems to work most of the time. If people say hi/hey/hello to me, I’ll generally return the favour. I like compliments as well, although I’m conscious of not coming on too strong, so I might not give a compliment straight away. As an introvert, I tend to overthink things, so when in doubt, I just start by saying hey.
Now keeping up a conversation, that’s the real challenge. I think I’m pretty good with holding a conversation, but I find it hard to feign an interest. I also don’t want to bore people with my niche interests either.