I'm not too old (24y) and thus don't have lots of experience(2 long term relationships, one still going). But if I gave advice, it'd be something like this:
First, try to identify what kind of girl you would like to have beside you with as much accuracy as possible. For example, my prerequisites for any girl:
1)take care of themselves physically (have some exercise during the week, eat well, sleep well, etc)
2)take care of themselves mentally (allow themselves free time each week to hang with friends, or watch an interesting documentary or read a book)
3)are intelligent. Actually I would prefer her to be a bit more intelligent than me, it'd give me something to learn.
These are the characteristics that I find essential to her. It will make me like her or make her a friend of mine, but not fall in love with her. To that:
1) She has an open mind. I don't care about her dogmas or disorders or anything (unless they somehow affect me) but I ABSOLUTELY INSIST that she is willing to discuss everything. If this is not the case, I could never maintain a relationship with her. One reason I like long term relationships is that I learn everything I can about the person. It makes me better too. If she is not willing to let me know her, then I lose this.
2) She leaves me alone when I ask her. Of course I too have no problem to discuss anything, but there may be not enough time! I WILL continue any conversation she asks me but there may be more pressing matters at the moment (like homework). I want her to understand that.
After that, I consider some things as a bonus like:
1) She likes to achieve. I like that too and that makes us understand each other.
2) She studies the same things. In this I am lucky, my girlfriend and I are in the same undergrad. We can NEVER find moments when there is nothing to discuss. On the other hand someone might find it a disadvantage that we mix work with a relationship, and sometimes it is.
Well there you are. Have your own list of things you look for! After that it's pretty easy, all you have to do is to develop strategies to attract that kind of girl. That comes only with experience, but not too much. Don't feel bad if you fail sometimes, just live and learn! Don't get attached too soon or you might get hurt. Also know that what you look for in a mate changes with time.
For example such a girl as I have described above certainly likes an intelligent conversation. Try reading philosophy and bringing it in a conversation. Don't go too far since some people might freak out if you go on them like "there is no god" or "the world might be a dream". People don't like it when you doubt their most basic believes, especially if they don't know you well enough. If you study the same things, this should be much easier. Also this gives you an incentive to be a good student, if you can outsmart her in certain subjects, she will certainly be interested! But don't belittle her.
Anyway I have been writing for too long, but I think I gave an idea of what I mean!