Marrakesh Oil by Earthly Body. I was given this by a friend who worked for folica.com and started using it a few years ago. It will take a few months to see the difference, but it took my hair from frazzled and dry tips to smooth and extends the time between haircuts (for me anyway). Use it every day from the tips to halfway to your head, running through damp hair with your fingers and especially before using heat on your hair.
Reasonable if common advice on how to make fine hair appear fuller; makes general recommendations.