I admit that sometimes I think as much about opening lines as I do about the title itself, which is to say that I think quite a bit about both. There's just something about both, and the way that each is, in its own way, what people always end up noticing first.
Is the title catchy and interesting?
Does the first line induce me into wanting to read more?
Having a good title and good opening line might actually be as important as actually having a good book in getting people to pick it up and buy/read it.
I don't know that I'm actually any good at putting it into practice, but it is something that I've noticed I pay more attention to lately.