Talk about stuff from their profiles and then when you run out of that stuff to talk about and they seem interesting, ask them out. No need to beat around the bush too much about it. Also, look for how engaged they are in the conversation. If they are giving one or two word answers and not asking any questions of their own, then they are not interested and just being polite.
Remember: There are 3.5 billion men and 3.5 billion women on this planet. No need to beat yourself up if someone isn't interested. There are literally BILLIONS of "fish in the sea".