If you ask me what makes a person lovable, I don't think I can give you a perfect answer.
But I have to say that everytime I saw somebody noticing details, I grew fonder of that person.
Like when you are on the phone or interacting on social network with them, they don't necessarily response to you immediately everytime but they never make the absence too long for you to feel awkward.
And they never send voice-mail to you when they know you're in the middle of some important occasions or when you're on the subway, because they know that it will make it very inconvenient for you and that text is the more appropriate choice.
They never let a conversation die, but they know when to stop.
And while they're pretty good listeners, they also have their own mature thoughts and would love to share them if they think the it suits the situation.
So, I can't really tell you what makes a person lovable, but I recognize one when I see one.
And I believe that everyone of you can do that, too.