I have long, weak, thin hair but generally healthy. how can i get some more volume and strengthen it

You should try to go to an Indian store and look for some henna. It's only about 2 dollars and can add some extra volume to the hair. You can also order henna online at hennaforhair.com but that costs more.As for straightening the hair a healthy way to straighten hair not to mention get some volume is to use rollerset method. Put big magnetic rollers on damp well conditioned hair than sit under hooddryer or let it air dry naturally, than comb out. Your hair should be relatively straight with plenty of volume.

I have long, weak, thin hair but generally healthy. how can i get some more volume and strengthen it?

seamless layers and backcomb, backcomb, backcomb