This is the key for any sensible man. You don't even need the rest. Women do one of two things, in my experience. Even if they make eye contact, that's no assurance they're interested. Sometimes, they'll quickly look away. But if the look holds, there's interest.

Unfortunately, I was a bit shy when I was young and that wasn't always enough.

There are countless guys who treat the male/female relationship like a sales call. 98% of them fail, but they're fine with that 2% that don't. So they just don't care how they come off.