I've developed my own thoughts about creepiness, since coming across as creepy is one of my biggest fears.

1) The theory of mirror neurons. This theory states that if you are nervous, the other person will pick up on it subconsciously. As the article states, false confidence, even if you try your best to hide it, will come across as a barely disguised nervousness.

https://en.wikipedia.org/wiki/Mirror_neuron

One of the things that I've observed while watching some pick-up artists practice is that those who eventually become "successful" are basically asking nothing of those who approach. They don't fear rejection. In fact, they can be quite entertaining and good listeners. However, for most of these individuals, they probably had to go through a lot of rejections to get to the point where they didn't honestly care what the reaction was.

2) The hover zone/kill zone

Commonly used in pick-up artist terminology. This is easily described as wanting to talk to a specific individual, even approaching within several feet, yet not doing it. I know we've all done this, at some point, at a bar or even at a friend's party. You know the person knows that you are interested in them.

3) Reciprocity

In one of Pedro Almodovar's movies, in the director's commentary on the DVD, there is a man in a woman's apartment who is looking through his host's stuff. The director makes a statement along the lines that "liking without reciprocity" makes it stalking (or worse).

In the very rare times, where a woman who has explicitly hit on me, asking lots of questions, showing interest that is out of norm with the pace of conversation (e.g. we just met), I can attest that it feels creepy as in (What have I done to make you so interested?). In more common circumstances, I recall people who are seemingly interested in you but quickly steer the conversation to something like network marketing.

Given these factors, what can be done to not come across as creepy?

First, don't hover. Talk to someone right away, even if it just a quick introduction.

Second, being quiet can actively work against you in most social situations. Especially when you are meeting new people. To this day, I can be enjoying a party by meeting new people in a group and listening to their stories and (usually) extroverts will ask if "are you having a good time?". Even if I am, it doesn't outwardly show, at least in the manner they'd expect.

Third, the answer may lie in being mindful of reciprocity. For example, talking to a cute individual, what is it about him/her/they that you find interesting (that is not related to something she cannot easily change, like her looks).

When I've talked to my good looking friend girls, they basically say they have to ignore all the attention/cat calls when they walk down the street.

Fourth, to escape the friend zone, you have to make it explicitly clear that you are interested in someone romantically and tell them why. Asking someone out to coffee to talk about their job v. asking someone out to a picnic because you like them.

One last side note - if you walk into a party with a couple good looking friends (male or female), people will automatically ascribe a higher status to you, whether you care to agree with the theory and practice of social proof or not.