How to tell if a guy is a jerk or a nice guy?

What are tests that can be perform to know if a guy is a jerk or a nice guy? I am crushing on a guy and he doesn't seems smart. He is smart. He doesn't seems stuck up but he seems like a "know it all" regarding finance. That is his undergrad major and he is a master program. He also is working for a finance company. I don't know how to stoke his ego or really talk to him since it is really hard for me to talk to guys I like. Advice? What line opening? Flirting tips? This is kind of sad bc it is so awkward for me.