How to get big hair?

I have thick hair and it annoys me to no end that after I straighten it it just falls flat against my head and looks thin. I can't figure out what to do, the internet keeps telling me to use curling irons but my hair just ends up falling back down like nothing was done to it. I don't know if I'm just not leaving the iron against my hair long enough or I'm not doing it close enough against my sclap or what.