Ok, so I'm not a curlygirl, but the stringy look is a characteristic of fine hair in general. Good conditioning is the key to combatting it in my experience. Hair has to have enough of a protective coating to prevent strands from rubbing and sticking together as much as possible. Oil works for some people, cones work for others.

Also, keeping your hair well groomed when you wear it down will prevent the stringy sitch. Because fine hair tangles easiest, it has to be detangled often. Wearing your hair in a contained style will prevent you from having to detangle so often if you don't wish to.

As for making fine hair thicker, wouldn't that be nice, eh? But I'm afraid you know as well as I do that there is no real way to do that. You can make your hair look and feel as thick as possible by just taking good care of it. Treating it carefully and "feeding" it properly - again, good conditioning is crucial here.

And did I mention regular trims? They are absolutely essential. I must get them every 3-6 months or my hair becomes a real nuisance to deal with! Ratty ends = ratty hair.

HTH