I have very soft, fine, thin hair. The only blessing is that I have a TON of it so with the right cut, it looks like I've got thick hair!! Until someone feels it.
First off, you have to think about cut. Thin, fine hair works with just a few cuts:
1. Very long, one layer. This will weigh the hair down but since you don't really "do" anything with it, it works. My DD has this and she gets a blunt cut on the ends, versus layer the ends and it appears thicker. You can put a volumizing mousse at the roots and dry upside down for root fullness. The dry shampoo is always a good idea at the roots. You can spray this in after you style.
2. Chin length, graduated "bob" style with severe undercutting. This will provide lift to the hair. In this style, you soft, silky hair is an advantage because it is usually very shiny and this looks great in this style.
3. A shorter/layered cut. Lots of layers. I do this because I'm pushing 50 and, after trying to grow my hair out and having "older" hair, it's just not great in the "hanging" mode. There's lots of volumizing products out that work great on short hair (but tend to gunk up the longer styles).
4. Foil highlights: the lighter the better. Highlights (with bleach versus a color) rough up the hair shaft and make your hair more coarse. This will help your style hold better. Of all the things, this works the best for me.
5. A 3 minute perm!!! I haven't tried this yet but my stylist tells me she does this for some of her fine-haired clients. You do a regular perm but you only leave in about 3 minutes so you don't get a hard curl. You just get some body and a whole lot of texture. Because it's just some body, you can easily blow it out if you want a straight look. If you are getting highlights, you can't do both at the same time.