In general, the things I find attractive are, in order from most-to-least important:
1. Sweetness, defined here as a nurturing, feminine quality characterized by (emotional) generosity and kindness.
2. Mutual attraction (I have trouble being attracted to someone if I don't get the sense that they are equally or more attracted to me)
3. Adventurousness. I've never dated a really adventurous girl, but I get really turned on when I meet a girl who's going places and doing fun things and has an appetite for adventure that's slightly higher than mine. It makes me feel like I need to chase them and try to keep up and like I might get taken for a super fun ride. I kind of imagine this would get exhausting after a while, though.
This is a pretty universally attractive quality. Everyone wants to hang out with someone that will show them new things and take them new places.
4. Physical qualities: big, bright eyes, short, dark hair (curly or messy is best) smooth skin.
5. Expanded world view. As an American it's really easy to maintain a tiny scope of awareness. (TV shows and shopping?!) So I pop mad boners when a lady can speak at length about: science, literature, geography, politics, philosophy or certain other facets of culture. However, I'm an obnoxious know-it-all, so I don't get too caught up on this one.
Turn offs (discovered from past dating)
1. Lack of adventurousness, sheltered, closed minded attitudes, fear. I want someone who is up for anything.
2. Girls that don't care about music. (I'm obsessive, so this is a common problem)
3. Girls that can't stay up late.
4. Girls that cross the threshold of independence and simply don't need anyone, emotionally. Good for them, but I can't be attracted to someone that has no room in their life for a +1
5. Talking too much . . . yup, sounds trite and/or misogynistic, but it's a pet peeve.
EDIT:
to answer OP's question more specifically, in allowing myself to be more attractive to others, #3 on my list of attractive qualities is the one that has helped me the most. If you want people to like you, you have to offer something interesting.
In the negative column, a common mistake I see in my fellow dudes is "coming off as desperate" if you like someone, just calm the fuck down and try to pretend you don't care that much. Pay attention to them, sure, but if you focus on them too much it sends up a psychological red flag.